I've been playing a contralto / contra-alto clarinet for a few years now and have often wondered about the variety of names for the instrument. When we are talking about instrument names, I think that it's helpful and necessary to look at other related languages for perspective. If we start with the stringed instrument, the double bass:
English: double bass
German: Kontrabass
French: contrebasse
Italian: contrabbasso
In this case, English prefers the qualifying "double" to denote being lower than a bass, but the three other languages use the prefix "contra". Some performers do use the term "contrabass" in English, but this is rarer that "double bass" or just "bass". Wind orchestra scores will use the term "string bass" to distinguish it from the other bass wind instruments.
English: contrabassoon
German: Kontrafagott
French: contrebasson
Italian: controfagotto
Again, the prefix "contra" indicates being lower than a bassoon, in this case, an octave lower. This connection between octave and contra is applicable here, but not necessarily in the case of the double bass/contrabass, because not all double basses have a low C extension or fifth low C string, and the tuning of the strings ((C), E, A, D, G) in all cases is not simply one octave lower than cello (C, G, D, A). The contrabassoon is sometimes called a double bassoon in English, but less often.
So in terms of the usage of the prefix "contra" with our beloved contralto/contra-alto clarinet, contra is useful in the sense that it tells us that this is instrument is both lower and an octave lower than the alto clarinet. In terms of range, contra — which also applies to the range of pitches between C1 and B1 (the lowest complete octave of the piano) — is an apt term for the instrument because its range extends downwards to either sounding contra F#1 or contra Eb1, in both cases covering at least half of the contra octave. The instrument can therefore function as a contra-instrument, in absence of a contrabass clarinet, providing octave support for the bass and alto clarinets or functioning alone as the bass/pedal.
Then we come to the tricky bit: contralto or contra-alto?
To my mind, the clarinet family has completely departed from any kind of correlation to the family of vocal ranges. The saxophone family somehow makes sense, because the instruments' transpositions are so well organised, being predominantly in Bb or Eb (soprillo in Bb, sopranino in Eb, soprano in Bb, alto in Eb, tenor in Bb, baritone in Eb, bass in Bb). Clarinets are all over the place, and there is one main problem: the so-called alto clarinet is in the position of a tenor clarinet. Indeed there are "tenor clarinet" projects with instruments pitched higher than an alto clarinet. For this reason, an adherence to vocal ranges when naming clarinets is a particularly fraught task.
English: alto clarinet
German: Altklarinette
French: clarinette alto
Italian: clarinetto contralto (!!) --> also sassofono contralto (in Eb) & flauto contralto (in G)
Here we run into a problem: Italian has for some reason gone with the term contralto to designate the nominal range of the alto clarinet and alto saxophone. "alto" simply means "high", which for an English-speaker sensibility is somewhat grating, because we associate the term "alto" with the idea of "less than high". Perhaps the contra-prefix in this case refers to both instruments' ability to play much lower than the alto vocal range (alto clarinet down to F#2 and alto saxophone to C#3), however this wouldn't apply to the alto flute (flauto contralto) because its low range corresponds exactly with that of the vocal range. According to the Italian Wikipedia, the term "contralto" relating to the alto vocal range is a shortening of the much older term "contratenor altus" and is simply the Italian equivalent of the word "alto/Alt" in other Western European languages. However, in all three cases (clarinetto contralto, sassofono contralto and contralto (voice type)) it is indicated that the shortened form "alto" is also in use. It may be a matter of time until this term in Italian is eroded to simply "alto", thanks also to globalisation. In the English language however, the eliding of the prefix contra- with the vocal range determiner that starts with a vowel, in this case "alto", is a standard linguistic manoeuvre and literally means "lower than alto" (the eliding of contra- and -bass is not possible due the consonant at the start of "bass"). So a contralto clarinet in any and every single case, is a clarinet that is pitched lower than the alto clarinet and has nothing to do with the vocal range, because the clarinet is not a voice. If we take into account the usage of the prefix contra- in instrument nomenclature (and in the English language, disregarding Italian for a moment) then contra- pertains to instruments that are either lower or an octave lower than their counterparts. The combination of both of these factors leads to the term, when used in English, "contralto".
If we briefly look at the names in the construction of low clarinets:
Leblanc: in the advertising material of the original Leblanc low clarinets in EEb and BBb the terms contra-alto and contrabass (in French, contre-alto and contrebasse) were preferred.
Selmer: in the advertising material of the rosewood instruments in EEb and BBb the terms contralto and contrabass (in French, contralto and contrebasse) are preffered.
Buffet: only make contralto/contra-alto clarinets and their website is in three of the above discussed languages: English: contra alto clarinet (without hyphen); German: Kontraaltklarinette; French: clarinette contralto
Evidently these three manufacturers also cannot agree on the nomenclature, the French terms actively disregarding the possible confusion with their Latin-based language neighbours, Italy.
As a professional performer who deals with these problems on a daily basis, I have come to refer to the clarinet family using the following groupings and terms:
high-range clarinets:
piccolo clarinets in D/Eb/G/Ab --> avoiding soprano/sopranino (DE: kleine; FR: petite; IT: piccolo)
clarinets in A/Bb/C --> avoiding soprano, they don't need a qualifying voice-type, it's a clarinet.
basset clarinets in A/Bb --> referring to the extended range of the standard instrument (basset derived from the Italian bassetto meaning “small bass”)
mid-range clarinets:
clarinet d'amore in G --> historically referenced term for G clarinets with a bulbous bell (also clarinet d’amour, clarinetto dolce)
basset horns in F/G --> surprisingly, this term, now over 300 years old, hasn't been modified or questioned even though today’s instrument is a significant departure from the earliest, curved instruments with a horn-like bell
alto clarinet in Eb --> one could also argue that this is a tenor and not an alto clarinet, but it’s really both. Having the same transposition as the alto saxophone, and yet, being closer in tessitura to the bass clarinet (which would render it a tenor instrument). The alto clarinet is the only surviving instrument from a group of alto-like instruments, having nominal pitches anywhere from D3 (d) to Ab3 (a♭) and still being called an alto clarinet. When you consider that almost all clarinets can function as alto instruments thanks to the generally large range of a clarinet, then whether this instrument is truly an alto or tenor clarinet is a moot point.
low-range clarinets:
bass clarinet in Bb --> "bass" in woodwind instruments most often equating to one octave lower than the standard instrument (bass flute in C, bass oboe in C)
contralto clarinet in Eb --> one octave lower than the alto clarinet
contrabass clarinet in Bb --> one octave lower than the bass clarinet
Check out my “map of the clarinet family” for more information!