What does 'chip in' mean?

[Lia39]

English Language Tests, Intermediate level

ESL/EFL Test #882 "Winning the Jackpot!", question 7

My co-workers ......... in fixed amounts of money and play the lottery, as a group, on a weekly basis.

(a) chip
(b) venture
(c) wager
(d) bet

English Language Tests, Intermediate level

ESL/EFL Test #882 "Winning the Jackpot!", answer 7

My co-workers chip in fixed amounts of money and play the lottery, as a group, on a weekly basis.

Correct answer: (a) chip

Your answer was: incorrect
My co-workers wager in fixed amounts of money and play the lottery, as a group, on a weekly basis.
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My co-workers chip in fixed amounts of money and play the lottery, as a group, on a weekly basis.

Hello.
I really don't understand the meaning of the word "chip" in this sentense. Can somebody help me?
Thanks a lot.

[Our Tort System]

The expression is "to chip in".
It roughly means "to donate/contribute".
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