Skimpy beachwear like a G-string (5)
I believe the answer is:
thong
This clue is a double definition.
'skimpy beachwear' is the first definition.
(I've seen this in another clue)
'g-string' is the second definition.
(type of underwear)
'like a' acts as a link.
(Other definitions for thong that I've seen before include "flip-flop" , "Skimpy underwear" , "Narrow strip of leather - beach garment" , "Strap - strip" , "article of clothing" .)