Meaning of 'petty cash'

[wael]

Test No. incompl/advan-12 "Money", question 3

Every office has a certain amount of ......... cash to pay for things like tea, coffee or stamps.

(a) small
(b) little
(c) tiny
(d) petty

Test No. incompl/advan-12 "Money", answer 3

Every office has a certain amount of petty cash to pay for things like tea, coffee or stamps.

Correct answer: (d) petty

Your answer was: incorrect
Every office has a certain amount of tiny cash to pay for things like tea, coffee or stamps.
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Hello Sir,
why can't we use tiny? tiny means little, small...

[Torsten]

Petty cash is a set phrase - a fixed combination of words. As you might know petty cash is a cash funds for incidentals, that means, you pay with it for small things.
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