Cut the grass three times (6)
I believe the answer is:
thrice
'three times' is the definition.
(synonyms)
'cut the grass' is the wordplay.
'cut' means to remove the last letter.
'grass' becomes 'rice' ().
'the' with its last letter taken away is 'th'.
'th'+'rice'='THRICE'
(Other definitions for thrice that I've seen before include "Three-time" , "as it can be found in little titbits" , "Once, once more and yet once more" , "Several times" , "In threefold degree" .)