Undertake to do it and you'll catch it! (8)
I believe the answer is:
contract
'undertake' is the definition.
(I know that undertake can be written as contract)
'do it and you'll catch it' is the wordplay.
I cannot quite understand how this works, but
'do' could be 'act' (I've seen this before) and 'act' is found within the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
The remaining letters 'cor' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'to' is the link.
Can you help me to learn more?
(Other definitions for contract that I've seen before include "Pick up" , "settlement" , "Make smaller" , "Agree - get smaller" , "Shrink in written agreement" .)