Risky thing to do in a tube train (3)

I believe the answer is:

bet

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'risky thing to do' is the definition.
I can't tell whether this defines the answer.

'in a tube train' is the wordplay.
'in' indicates a hidden word.
'BET' can be found hidden inside 'tube train'.

Can you help me to learn more?

(Other definitions for bet that I've seen before include "Wager, or the sum waged" , "Wager, speculate" , "Money risked on a gamble" , "Wager, gamble" , "Wager, back" .)

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