Tim's pig eating roughly double (8,5)
I believe the answer is:
spitting image
'double' is the definition.
(thesaurus)
'tim's pig eating roughly' is the wordplay.
'roughly' indicates an anagram.
'tims'+'pig'+'eating'='timspigeating'
'timspigeating' is an anagram of 'SPITTING IMAGE'.
(Other definitions for spitting image that I've seen before include "Perfect likeness" , "show on TV" , "exact copy" , "Exact double" , "Exact likeness" .)