United game almost different in size (9)
I believe the answer is:
magnitude
'size' is the definition.
(thesaurus)
'united game almost different' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'different' indicates anagramming the letters.
'united'+'game'='unitedgame'
'unitedgame' with its final letter taken away is 'unitedgam'.
'unitedgam' anagrammed gives 'MAGNITUDE'.
'in' is the link.
(Other definitions for magnitude that I've seen before include "Largeness or size" , "(A star's) brightness" , "Dimensions" , "Relative importance" , "Eating mud (anag.)" .)