A rope, but not a second as well (4)
I believe the answer is:
also
'as well' is the definition.
('also' can be a synonym of 'as well')
'a rope but not a second' is the wordplay.
'rope' becomes 'lasso' (lasso is a kind of rope).
'but not' suggests deleting specific letters.
'a second' becomes 'as' (I've seen this in other clues).
'lasso' with 'as' taken away is 'lso'.
'a'+'lso'='ALSO'
(Other definitions for also that I've seen before include "admitted to Royal Society > too" , "As well, in addition" , "in accompaniment" , "What's more" , "revolutionary a part for Yugoslavia" .)