unicorn

a horse-like fabled animal that has one horn growing out of the middle of its forehead

unicycle

a one-wheeled vehicle on which the rider sits and pedals

unison

an instance of saying the same words or sounds at the same time; a group that sounds like one

unilateral

one sided

unique

one of a kind; unusual or rare

unify

to join together into one group

unidirectional

moving in only one direction

unitard

a one-piece leotard and tights combination

unit

one group

unicellular

having only one cell