I have a short composition and I would like to give it a name but I don't know what term would be more appropriate (Suite, Sonata, Partita, another one?). The composition has a duration of 1:21, uses violins (melody and harmony) and most likely won't have other pieces as a continuation. What is the best name for that kind of short independent piece?
The tentative name would be "X in C Major", where X is the suitable term.
Names of the type asked about depend wholly on the purpose, structure, or musical character of the piece, not its duration. Given that the piece is written for two violins, then the most appropriate title would be:
Violin Duet in C Major
Other options might be
Of the titles specifically mentioned,
A Suite is a baroque Form that is a collection of dances. So a Suite consists of multiple pieces. A Partita is a part of a Variation, but is also used in a Suite-like manner or even for any instrumental pieces. A Sonata originally implied a form and a structure, which has somewhat faded over time.
A modernist approach would be to not give a name at all and just call is a "piece in C major for ...". Quite common would be to simply designate the number of players (Duet, Trio, Quartet, Quintet, Sextet, Septet, Octet, ...). You can designate the form of the piece (Dance, Minuet, Variation, Melody, Chorale, ...). You can designate a form stolen from a different form of art (Literature: Proloque, Epiloque, ...). You can designate an implied meaning of the music (e.g. Liszt La prédication aux oiseaux). You can designate a term for the shortness of the music (Miniature, Bagatelle).
So in your case considering the music is short and has few instruments you could say Miniature in C major for X violins.
Mentioning the key is only required if there is nothing else allowing distinction, I would not suggest it. (Except when writing for beginners, which are easily intimidated by accidentals.) There is an extra question concerning the key in titles here.
Some choices:
Originally sonata was used for anything without voices (see Domenico Scarlatti) , presence of voices would have made a cantata, but since the sonata form appeared, the meaning got much more specific.
Suite, as in Baroque suite, is a group of several dance forms usually unified by sharing the same key but differing in meter and tempo. Number of movements varies but allemande, courante, sarabande, gigue are the basic ones.
Sonata has a meaning which has changed over time, but the common use if for either sonata allegro form (formal sections of exposition, development, recapitulation) or a work that usually has at least one movement in that form.
Partita is basically the same thing as suite.
You can go on and on like this just listing descriptions, but if you didn't consciously write in a form or genre, why do you want to use terms like sonata, suite, etc. in the title? How would it be meaningful to apply one of those labels if you don't know what they mean? Sorry to be blunt, but to do that seems a bit pretentious.
You don't have to give form and key in your title. And if your work wasn't really meant as a formal example of something, I don't think it makes much sense to give it that sort of formal title.
In classical music many works were not really titled by the composers. The titles came later when published. And sometimes those titles were really plain, like 12 Waltzes (with an opus number that was really a publishing number) and each waltz just 1, 2, 3...
Sometime works will fit a clear form, for example ternary form, but those works may get picturesque titles. Debussy wrote two books of piano preludes, most of which are in ternary form, but they all got evocative title like The Girl with the Flaxen Hair, or The Sunken Cathedral, etc.
Why not just title it by what it means to you? Or just do something like finish the sentence: "I wrote a...", and make that the title. In comments you said: It just used 3 chords and recorded it. It seems baroque to me.
Why not a title like this? Impressions of the Baroque Using Three Chords.
