Get into a pool (3)
I believe the answer is:
bet
'get into a pool' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for bet that I've seen before include "Money risked on a gamble" , "Wager, speculate" , "'Stake, wager (3)'" , "Wager, back" , "22 across will accept one" .)