Saw always cuts grass (6)
I believe the answer is:
saying
'saw' is the definition.
(thesaurus)
'always cuts grass' is the wordplay.
'always' becomes 'ay'.
'cuts' means one lot of letters goes inside another (some letters cut their way into other letters).
'grass' becomes 'sing' (I've seen this in other clues).
'ay' inserted within 'sing' is 'SAYING'.
(Other definitions for saying that I've seen before include "Apophthegm" , "Saw" , "Motto" , "Uttering" , "Expressing in words" .)