Linguists use the term "formant" to refer to refer to those frequency components that e.g. distinguish one vowel from another. Typically, we refer to F1, F2, F3, and F4 and their role in determining the articulatory mechanism used to produce a phoneme or phonemes.
Obviously, there are no phonemes in instrumental music. In what sense, then, if any, is the concept of "formant" comparable?