Boy tries to create gravity (8)
I believe the answer is:
sobriety
'gravity' is the definition.
(synonyms)
'boy tries to create' is the wordplay.
'to create' indicates anagramming the letters.
'boy'+'tries'='boytries'
'boytries' with letters rearranged gives 'SOBRIETY'.
(Other definitions for sobriety that I've seen before include "Refraining from" , "restraint" , "Abstemiousness" , "Calmness -- 8 -- by Tories (anag)" , "Calmness, dispassion" .)