Anyhow, I can’t hold on or hold back (7)
I believe the answer is:
contain
'hold back' is the definition.
('contain' can be a synonym of 'hold back')
'anyhow i can't hold on' is the wordplay.
'anyhow' indicates an anagram.
'hold' is an insertion indicator.
'i'+'cant'='icant'
'icant' anagrammed gives 'ctain'.
'ctain' placed around 'on' is 'CONTAIN'.
'or' acts as a link.
(Other definitions for contain that I've seen before include "Control, restrain" , "Accommodate" , "Keep within limits or have within" , "Carry" , "keep within bounds" .)