Lose one's cool' is an idiom that means to become angry or frustrated. The crossword solutions for this term include PANIC (5 letters), FLIP (4 letters), SNAP (4 letters), RANT (4 letters), RAVE (4 letters), THAW (4 letters), ERUPT (5 letters), GOAPE (5 letters), STEAM (5 letters), GETMAD (6 letters), SEERED (6 letters), HAVEAFIT (8 letters), THROWAFIT (9 letters), BLOWAGASKET (11 letters), and FLYOFFTHEHANDLE (15 letters). These words all describe different ways of expressing anger or frustration, such as panicking, flipping out, snapping at someone, ranting, raving, thawing out, erupting, going ape, steaming, getting mad, seeing red, having a fit, throwing a fit, blowing a gasket, and flying off the handle.