Ruler's dress held by promoted crawler (7)
I believe the answer is:
tsarina
'ruler's' is the definition.
(I've seen this before)
'dress held by promoted crawler' is the wordplay.
'dress' becomes 'sari' (sari is a kind of dress**).
'held by' is an insertion indicator.
'promoted' says the letters should be written in reverse (going up, in a down clue).
'crawler' becomes 'ant' (an ant crawls).
'ant' backwards is 'tna'.
'sari' going into 'tna' is 'TSARINA'.
(Other definitions for tsarina that I've seen before include "Russian empress (S, not Z)" , "companion of emperor" , "aristocratic woman" , "Russian royal; Sinatra (anag.)" , "Consort" .)