Gravity is an attractive quality (9)
I believe the answer is:
acuteness
'gravity' is the definition.
(I've seen this before)
'an attractive quality' is the wordplay.
'an' becomes 'a'.
'attractive' becomes 'cute' ('cute' can be similar in meaning to 'attractive').
'quality' becomes 'ness' (I've seen this in other clues).
'a'+'cute'+'ness'='ACUTENESS'
'is' is the link.
(Other definitions for acuteness that I've seen before include "gravity" , "Use secant with sharp perceptiveness" .)