Advice about extremely unusual flower (5)
I believe the answer is:
tulip
'flower' is the definition.
(thesaurus)
'advice about extremely unusual' is the wordplay.
'advice' becomes 'tip' (I've seen this before).
'about' is an insertion indicator.
'extremely' suggests removing the centre.
'unusual' with its centre removed is 'ul'.
'tip' placed around 'ul' is 'TULIP'.
(Other definitions for tulip that I've seen before include "Spring-flowering plant" , ""Dutch" flower" , "Flower - lit up (anag)" , "Liliaceous bulb" , "Bulbous plant" .)