This word is acceptable for play in the UK dictionary that is being used in the following games:

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adj. On the underside of the tail.

adj. Situated under, or on the ventral side of, the tail.

Situated under the tail; placed on the under side of the tail: as, subcaudal chevron-bones; the subcaudal scutes, or urosteges, of a snake.

Not quite caudal or terminal; situated near the tail or tail-end; subterminal.

n. That which is subcaudal; specifically, in herpetology, a urostege; one of the special scutes upon the under side of the tail of a serpent.

"This high-principled lophobranch is so careful of its callow and helpless young that it carries about the unhatched eggs with him under his own tail, in what scientific ichthyologists pleasantly describe as a subcaudal pouch or cutaneous receptacle."

subcaudal pouch   

subcaudally