(idiomatic) Under great pressure to perform.
Synonyms: under the cosh, (Australia, New Zealand) under the pump
He was under the gun to finish the project quickly.
(poker) Of, pertaining to, or in the situation of first player to act on the first round of betting.
Synonym: UTG
James will be under the gun for the first hand of the final table.
(obsolete, military) Too close to be subject to artillery fire.
Source: en.wiktionary.orgSometimes I think that TV evangelism is one of Satan's greatest weapons. They put these guys on a pedestal and all of a sudden they get caught with a prostitute, and every Christian I know then is under the gun. So you don't think that's kind of set up? Alice Cooper
I don't know what it is, exactly, but there's a negative drag on film sets after the second week or so, a mutinous vibe because the infinite capacities of the directors and everybody else become quite finite and everybody's under the gun and it becomes work. Diane Lane