Effortless as moths flying round the ring (6)
I believe the answer is:
smooth
'effortless' is the definition.
(thesaurus)
'moths flying round the ring' is the wordplay.
'flying' indicates anagramming the letters (letters fly around into new positions).
'round' indicates putting letters inside.
'the ring' becomes 'o' (letter resembling a ring).
'moths' with letters rearranged gives 'smoth'.
'smoth' going around 'o' is 'SMOOTH'.
'as' acts as a link.
(Other definitions for smooth that I've seen before include "Not rough or coarse" , "Level; suave" , "Free from roughness, bumps etc." , "without difficulty" , "Free from roughness or irregularities" .)