Invariably, it can be five short (4)
I believe the answer is:
ever
'invariably' is the definition.
(thesaurus)
'it can be five short' is the wordplay.
I cannot quite understand how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is located in the answer.
'five' could be 'v' (roman numeral) and 'v' is found in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ever that I've seen before include "Continually" , "On any occasion" , "Veer away endlessly" , "Always, at any time" , "Eternity" .)