go off at half-cock is a verb meaning "act prematurely or without reflection or too soon". It carries one recorded sense.
act prematurely or without reflection or too soon
“she wanted to quit her job but her mother told her not to go off half-cocked”
Definitions, synonyms and semantic relations for go off at half-cock come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.