Source : Webster's Revised Unabridged Dictionary (1913)

Tetrameter \Te*tram"e*ter\, n. [L. tetrametrus, Gr. ?; te`tra-
   (see {Tetra-}) + ? a measure: cf. F. t['e]tram[`e]tre.] (GR.
   & Latin Pros.)
   A verse or line consisting of four measures, that is, in
   iambic, trochaic, and anapestic verse, of eight feet; in
   other kinds of verse, of four feet.

Source : WordNet®

tetrameter
     n : a verse line having four metrical feet