Unarticulate: not jointed nor segmented.
Unci: thick, hooked processes, forming the borders of the anal opening.
Uncinnate: hooked at the end.
Uncus: in Lepidoptera, Diptera, and elsewhere, the curved book directed downward from a triangular dorsal plate in the male and shielding the penis: the genital hamule.
Undate: wavy or waved.
Undulated: obtusely waved in segments of circles.
Unequal: unlike in size, form, development or other characters.
Ungues: the tarsal claws.
Unguiculate: armed with a hook, nail or claw.
Unguiculus: a small terminal claw or nail-like process.