- under arms
- under cover
- under construction
- u.s. waters
- unratable
- unraised
- unsynchronous
- unstriped muscle
- uncorrelated
- unhealthy conduct
- undecenoic acid
- ureterocele
- uterine prolapse
- unit record device
- unenviously
- universal genetic code
- undersealed
- undissociated
- uterine plexus
- unsaturated fat
- unsaturated fatty acids
- ubbelohdes apparatus
- unilatarel recurrent laryngeal paralysis
- under protest
- under way
- untravelled
- untraversable
- universally
- ulcerogenic drugs
- unpunishable
- uniovulate
- ulnocarpal dise
- unassertively
- unneighborly
- unisexual
- under the terms
- unindebted
- uneaten
- under attack
- unit string
- ultrastructural reaction
- unfeigned
- upstanding
- up to the mark
- upward
- untruthful
- unfair
- up the spout
- uselessly
- usurpation