Officially cool, acrylic, itchy trousers (5)
I believe the answer is:
licit
'officially cool' is the definition.
Both the answer and definition are adjectives. Maybe you can see a link between them that I don't see?
'acrylic itchy trousers' is the wordplay.
'trousers' indicates a hidden word (trouser can mean to steal or take).
'LICIT' is hidden within 'acrylic itchy'.
Can you help me to learn more?
(Other definitions for licit that I've seen before include "Not forbidden, lawful" , "OK?" , "Within the law" , "Acceptable" , "Legal" .)