Emily Dickinson Lexicon

PEN-TAM'E-TER, n. [Gr. πεντε, five, and μετρον, measure.]

In ancient poetry, a verse of five feet. The two first feet may be either dactyls or spondees; the third is always a spondee, and the two last anapests. A pentameter verse subjoined to a hexameter, constitutes what is called elegiac. – Encyc.