One bearing thong? Swimmer is lad showing cheek (14)
I believe the answer is:
whippersnapper
'one bearing thong? swimmer is lad showing cheek' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'one bearing thong? swimmer' is the wordplay.
'one bearing thong?' becomes 'whipper' (I can't justify this - if you can you should believe this answer much more).
'swimmer' becomes 'snapper' (snapper is a kind of aquatic vertebrate).
'whipper'+'snapper'='WHIPPERSNAPPER'
Can you help me to learn more?
(Other definitions for whippersnapper that I've seen before include "Nonentity" , "cheeky upstart" , "Presumptuous young person" , "Scallywag" , "Cheeky youngster" .)