Dressing lead actor in wet earth (7)
I believe the answer is:
mustard
'dressing' is the definition.
(condiment)
'lead actor in wet earth' is the wordplay.
'lead actor' becomes 'star' (eg the star of a show).
'in' is an insertion indicator.
'wet earth' becomes 'mud' (I've seen this in another clue).
'star' put inside 'mud' is 'MUSTARD'.
(Other definitions for mustard that I've seen before include "Plant" , "It gives a bit of a kick" , "Standard of keenness" , "The colour" , "The keen stuff ?" .)