Young bird lacks the vision to be smart (4)
I believe the answer is:
chic
'to be smart' is the definition.
(both can mean stylish)
'young bird lacks' is the wordplay.
'young bird' becomes 'chick' (I've seen this before).
'lacks' means to remove the last letter (I've seen 'lacking' mean this (the word is incomplete or lacking)).
'chick' with its final letter removed is 'CHIC'.
'the vision' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for chic that I've seen before include "Elegant and stylishly fashionable" , "cool" , "Unwanted sounds" , "Fashionably smart" , "Snazzy" .)