Adult shows new aim - leave (5)
I believe the answer is:
imago
'adult' is the definition.
(I've seen this before)
'new aim leave' is the wordplay.
'new' indicates an anagram.
'leave' becomes 'go' (to go is to depart or leave).
'aim' is an anagram of 'ima'.
'ima'+'go'='IMAGO'
'shows' acts as a link.
(Other definitions for imago that I've seen before include "Adult, post-metamorphosis insect" , "subconscious view" , "Insect at end of life" , "Last state of insect life" , "That's as far as a butterfly can go" .)