What does the idiom 'cool as culcumber' mean?

[CoolCu]

English Language Tests, Intermediate level

ESL/EFL Test #202 "Idioms about Food", question 4

Ray was as 'cool as a cucumber' about his exam because he studied all week for it. What does 'cool as a cucumber' mean? ..........

(a) To be scared and cold about something
(b) To be very embarrassed about something
(c) To be very calm and relaxed about something

English Language Tests, Intermediate level

ESL/EFL Test #202 "Idioms about Food", answer 4

Ray was as 'cool as a cucumber' about his exam because he studied all week for it. What does 'cool as a cucumber' mean? To be very calm and relaxed about something.

Correct answer: (c) To be very calm and relaxed about something
_________________________

why cucumber is used?

CoolCu

[Torsten]

Because the idiom 'to be cool as a cucumber' means 'to be very calm and relaxed'.

TOEIC listening, talks: Newspaper executive announcing extension of deadlines due to bad weather

[NinaZara]

Women put slices of cucumber on their eyes to relax. It's very cool and relaxing. If you're familiar with American movies, you can see scenes in a spa or beauty salon where women have mud and cucumber on their face. Maybe this can help you understand why cucumber is used.