U: uav, unas, urgo, urrone...

[Vern]

U.A.V.
U.A.V. stands for "Unmanned Airborne Vehicle". The SGC (Stargate Command) uses them for reconisense, aswell as missile targeting. They can also be mounted with their own missiles for offensive purposes.

Unas
Native to planet P3X-888, these large, primitive, reptilian humanoids — once used as Goa'uld beasts of burden — possess only rudimentary language. First contact with the Unas was in the episode "The First Ones".

Urrone

[CaptainHaz]

Unity

A sentient crystalline lifeform discovered by SG1 early in its history. This lifeform knocked Jack O'Neill unconscious and took his form and infiltrated the SGC and the local community.

[Vern]

Urgo (episode)
SG-1 steps through the Stargate on their way to a paradise planet and end up at the SGC. Adding to their confusion is Hammond's assertion that the team was gone for fifteen hours, not the mere moment that the SG-1 perceived.

Upgrades (episode)
Anise, a new Tok'ra representative to Earth, approaches the SGC for help in testing some mysterious armband devices discovered amongst the ruins of a distant planet.

Unnatural Selection (episode)
When the Asgard homeworld is overrun by Replicators, the team is unexpectedly called into battle.

Underground (episode)
McKay's efforts to harness the energy of an alien planet's atmosphere allows for a return trip to Earth -- but the team may not be able to return to Atlantis.