Heavy wig they are adjusting (7)
I believe the answer is:
weighty
'heavy' is the definition.
(I know that heavy can be written as weighty)
'wig they are adjusting' is the wordplay.
'are adjusting' is an anagram indicator.
'wig'+'they'='wigthey'
'wigthey' anagrammed gives 'WEIGHTY'.
(Other definitions for weighty that I've seen before include "having great influence" , "Important" , "significant" , "substantial" , "Cumbersome" .)