Invariably five short (3)
I believe the answer is:
eer
'invariably five short' is the definition.
Both the answer and definition are adverbs. Perhaps there's an association between them I don't understand?
'invariably five short' is the wordplay.
'invariably' becomes 'ever' (I've seen this in another clue).
'five' becomes 'V' (Roman numeral).
'short' is a deletion indicator (short can mean missing or absent).
'ever' with 'v' taken away is 'EER'.
Can you help me to learn more?
(Other definitions for eer that I've seen before include "Always (poetic)" , "Before, poetically speaking (1'2)" , "Ever poetically" , "Always (poetical)" , "Ever to the poet (3)." .)