1. become or avoid becoming angry at someone/something
Professional
Social
I lost my temper, he lost his head, I kept my cool
When you lose your temper, lose your cool or lose your head it means you have become uncontrollably angry or to fail to control your emotions or keep your composure and become angry instead. To keep your cool or keep your head means the opposite to remain calm and composed in difficult, stressful or upsetting circumstances.