Without afterthought, cops now stick together (6)
I believe the answer is:
cohere
'stick together' is the definition.
(to cohere is to stick or fit together)
'without afterthought cops now' is the wordplay.
'without' indicates named letters should be taken away.
'afterthought' becomes 'ps' (as in a PS in a letter).
'now' becomes 'here' (I've seen this before).
'cops' with 'ps' taken away is 'co'.
'co'+'here'='COHERE'
(Other definitions for cohere that I've seen before include "Form a whole" , "Even; without jerks" , "Cling" , "Stick or hold together and resist separation" , "Fuse together" .)