...putting "reserved" on half of it perhaps - that's odd (5)
I believe the answer is:
fishy
'that's odd' is the definition.
(thesaurus)
'putting reserved on half of it' is the wordplay.
I cannot quite see how this works, but
'reserved' could be 'shy' (I've seen this before) and 'shy' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'perhaps' acts as a link.
Can you help me to learn more?
(Other definitions for fishy that I've seen before include "Dodgy, suspicious" , "Arousing suspicion" , "Suspicious (as trout?)" , "Suspect" , "Dubious - piscatorial" .)