Having a share in? You bet! (5)
I believe the answer is:
stake
'bet' is the definition.
(I know that bet can be written as stake)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for stake that I've seen before include "Prize" , "Post; gamble" , "Amount gambled" , "Investment" , "stout support" .)