As a piece of land, it covers very little (6)
I believe the answer is:
bikini
'as' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for bikini that I've seen before include "providing little cover for swimmers" , "Small bathing costume or atoll in Marshall Islands" , "Two-piece cozzie" , "Infamous atoll" , "strip of beach" .)