The Collaborative International Dictionary of English v.0.48:

Spirant \Spi"rant\, n. [L. spirans, -antis, p. pr. of spirare to
   breathe. See Spirit.] (Phon.)
   A term used differently by different authorities; -- by some
   as equivalent to fricative, -- that is, as including all the
   continuous consonants, except the nasals m, n, ng; with the
   further exception, by others, of the liquids r, l, and the
   semivowels w, y; by others limited to f, v, th surd and
   sonant, and the sound of German ch, -- thus excluding the
   sibilants, as well as the nasals, liquids, and semivowels.
   See Guide to Pronunciation, [sect][sect] 197-208.
   [1913 Webster]

WordNet (r) 3.0 (2006):

spirant
    adj 1: of speech sounds produced by forcing air through a
           constricted passage (as `f', `s', `z', or `th' in both
           `thin' and `then') [syn: fricative, continuant,
           sibilant, spirant, strident]
    n 1: a continuant consonant produced by breath moving against a
         narrowing of the vocal tract [syn: fricative consonant,
         fricative, spirant]