Incredibly cool lass, huge (8)
I believe the answer is:
colossal
'huge' is the definition.
(I know that huge can be written as colossal)
'incredibly cool lass' is the wordplay.
'incredibly' is an anagram indicator.
'cool'+'lass'='coollass'
'coollass' is an anagram of 'COLOSSAL'.
(Other definitions for colossal that I've seen before include "Extremely large" , "So locals may be huge" , "Stupendous" , "Gargantuan" , "Huge, immense" .)