It’s apt to hold things up (4)
I believe the answer is:
mast
'apt to hold things up' is the definition.
I can't tell whether this defines the answer.
'it's' is the wordplay.
I cannot really understand how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found in the answer.
The remaining letters 'mas' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mast that I've seen before include "Television transmitter" , "Tall radio transmitter" , "Spar to support a sail" , "Supporting pole, for radio aerial, perhaps" , "Pole on ship" .)