Webster's Revised Unabridged Dictionary · 1913

Pentamerous

Pentamerous , adjective

[Penta- + Greek {not transcribed} part.]

1.
(Biology) Divided into, or consisting of, five parts; also, arranged in sets, with five parts in each set, as a flower with five sepals, five petals, five, or twice five, stamens, and five pistils.
2.
(Zoology) Belonging to the Pentamera.