'U'
Unbelievable A general expression of amazement
Underdaks Underwear
Undress a sheep To shear a sheep
Uni A university
Union jack A type of cicada
Up Up to specifications or up to standard. Used in the negative eg "not up" "not up to expectations"
Up a gumtree In a quandary
Up country The inland; the outback
Up King Street Bankrupt; in financial difficulties
Up shit creek Things are going wrong
Up there Cazaly A cry of encouragement. Cazaly was a noted South Melbourne footballer, whose specialty was high marking
Up to putty No good; worthless. Also "up to mud" "up to tripe"
Up you for the rent A contemptuous way of saying "get lost" 
Uphill Facing a difficult task
Upter No good; worthless
Upya A contemptuous way of saying "get lost" 
Urger A racecourse tipster; a trickster's confederate
Ute -a- A utility vehicle