Wordnet 3.0
NOUN (1)
1. 
 the syllable naming the fourth (subdominant) note of the diatonic scale in solmization; 
The Collaborative International Dictionary of English v.0.48:
Fa \Fa\ (f[aum]), n. [It.] (Mus.)
      (a) A syllable applied to the fourth tone of the diatonic
          scale in solmization.
      (b) The tone F.
          [1913 Webster]
WordNet (r) 3.0 (2006):
fa
    n 1: the syllable naming the fourth (subdominant) note of the
         diatonic scale in solmization
V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):
FA
       FernmeldeAmt (DTAG)