What's the origin of the phrase 'As cool as a cucumber'? Cool here means imperturbable rather than low in temperature, although the simile is formed by alluding to the coldness of cucumbers which, being mostly water, are cool to the touch. 'As cool as a cucumber' is first recorded in John Gay's Poems, New Song on New Similes, 1732:

The origins of the idiom “ as cool as a cucumber ” come from the 1700s. the phrase appeared in the work of the British poet John Gay in his poem, “ New Song on New Similes .” Gay penned the piece in 1732, with the phrase, “ Cool as a cucumber could see the rest of womankind .”