Initially, cup left a ring on the dress (6)
I believe the answer is:
clothe
'dress' is the definition.
(synonyms)
'initially cup left a ring on the' is the wordplay.
'initially' indicates taking the first letters.
'a ring' becomes 'o' (letter resembling a ring).
'on' is a charade indicator (letters next to each other).
The initial letters of 'cup left' is 'cl'.
'cl'+'o'+'the'='CLOTHE'
(Other definitions for clothe that I've seen before include "Provide cover for body and limbs" , "apparel" , "Provide with garments" , "Equip" , "robe" .)