Webster's Revised Unabridged Dictionary · 1913

Tergum

Tergum , noun

[Latin, the back.]

(a)
(Zoology) The back of an animal.
(b)
(Zoology) The dorsal piece of a somite of an articulate animal.
(c)
(Zoology) One of the dorsal plates of the operculum of a cirriped.