Therefore he got pleasant, wasting second (5)
I believe the answer is:
hence
'therefore' is the definition.
(synonyms)
'he got pleasant wasting second' is the wordplay.
'got' indicates putting letters inside.
'pleasant wasting second' becomes 'enc' (I am not sure about this - if you are sure you should believe this answer much more).
'he' going around 'enc' is 'HENCE'.
Can you help me to learn more?
(Other definitions for hence that I've seen before include "As a result" , "As a consequence" , "For this reason; in the future" , "It follows from that fact" , "Thus" .)