Custom corset occasionally revealing top (6)
I believe the answer is:
utmost
'top' is the definition.
(thesaurus)
'custom corset occasionally' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'custom'+'corset'='customcorset'
The alternate letters of 'customcorset' are 'UTMOST'.
'revealing' is the link.
(Other definitions for utmost that I've seen before include "(To the) greatest possible extent" , "At furthest limit" , "Extremest" , "Farthest" , "Highest in degree" .)