As cool as a cucumber is an idiom which means self-possessed, not excited, in control of one’s emotions. As cool as a cucumber is a simile, which is a figure of speech that compares one thing to another. The phrase as cool as a cucumber is first seen in a poem by John Gay in the mid-1700s. In fact, the inside of a cucumber in the garden may be as much as twenty degrees cooler than the ambient temperature. The idiom as cool as a cucumber is a play on two meanings of the word cool: a temperature trending toward the cold side and a state of being calm.
And, even when I received the e-mail a few weeks later that I obtained it, I was still as cool as a cucumber, but freaking out on the inside. (The Huffington Post)
The council estate kid in me screamed “HOW MUCH?!” a hundred times when reading over the menu, but the cool grown-up journalist façade remained as cool as a cucumber (mmm, cucumber), emanating the vibe of someone that has just stepped off a helicopter in Manolo Blahniks. (The Express and Star)
She was as cool as a cucumber when she was getting it cut, she was not scared and kept chatting. (The Gazette and Herald)
MAN Haron Monis spent at least an hour in the Lindt cafe before Monday’s bloody siege and was “as cool as a cucumber’’, according to one of the last people to speak to him before he seized control of the Sydney CBD venue. (The Australian)
“It matters not to Jamie and I would back him all day long – he is as cool as a cucumber. (The Mirror)