Slim elves play around the square (6)
I believe the answer is:
svelte
'slim' is the definition.
(I've seen this in another clue)
'elves play around the square' is the wordplay.
'play' indicates an anagram.
'around' is an insertion indicator.
'the square' becomes 'T' (a T-Square is a technical drawing instrument).
'elves' anagrammed gives 'svele'.
'svele' placed around 't' is 'SVELTE'.
(Other definitions for svelte that I've seen before include "Slender or sleek" , "Polished" , "Gracefully slender" , "Sylphlike" , "Gracefully slim" .)