Riding limited on island - it covers top and bottom only (6)
I believe the answer is:
bikini
'it covers top and bottom only' is the definition.
(garment covering one's top and bottom)
'riding limited on island' is the wordplay.
'riding' becomes 'biking' (biking is a kind of riding).
'limited' means to remove the last letter.
'on island' becomes 'i' (I am not sure about this - if you are sure you should believe this answer much more).
'biking' with its final letter taken off is 'bikin'.
'bikin'+'i'='BIKINI'
(Other definitions for bikini that I've seen before include "Small two-piece bathing suit" , "Atoll and skimpy swimsuit" , "Women's tiny bathing costume" , "Swimsuit for the beach" , "Site of A-Bomb tests; resultantly shocking swimwear!" .)