Nick a lot of this the day before (6)
I believe the answer is:
thieve
'nick' is the definition.
(I know that thieve has the is a more specific form of the action nick)
'a lot of this the day before' is the wordplay.
'a lot of' means to remove the last letter (a lot of but not all of the word).
'the day before' becomes 'eve' (eve is the night before something).
'this' with its last letter taken away is 'thi'.
'thi'+'eve'='THIEVE'
(Other definitions for thieve that I've seen before include "Rob" , "Pilfer" , "Misappropriate" , "Steal things" , "Nick things" .)