If coming up short, is suspicious (5)
I believe the answer is:
fishy
'suspicious' is the definition.
(synonyms)
'if coming up short' is the wordplay.
'coming up' says the letters should be written backwards (in a down clue, letters go up).
'short' becomes 'shy' (I've seen this in another clue).
'if' written backwards gives 'fi'.
'fi'+'shy'='FISHY'
'is' acts as a link.
(Other definitions for fishy that I've seen before include "Dubious - piscatorial" , "Suspicious (as trout?)" , "Arousing suspicion" , "Suspect" , "As smelt, perhaps" .)