Source : Webster's Revised Unabridged Dictionary (1913)

Pentameter \Pen*tam"e*ter\, n. [L., fr. Gr. ?; ? (see {Penta-})
   + ? measure.] (Gr. & L.Pros.)
   A verse of five feet.

   Note: The dactylic pentameter consists of two parts separated
         by a di[ae]resis. Each part consists of two dactyls and
         a long syllable. The spondee may take the place of the
         dactyl in the first part, but not in the second. The
         elegiac distich consists of the hexameter followed by
         the pentameter. --Harkness.

Pentameter \Pen*tam"e*ter\, a.
   Having five metrical feet.

Source : WordNet®

pentameter
     n : a verse line having five metrical feet