Emperor tricked, laughing briefly (7)
I believe the answer is:
hadrian
'emperor' is the definition.
(Roman emperor)
'tricked laughing briefly' is the wordplay.
'tricked' becomes 'had' (to have someone can mean to trick them).
'laughing' becomes 'riant' (riant can mean cheerful or laughing).
'briefly' means to remove the last letter.
'riant' with its last letter removed is 'rian'.
'had'+'rian'='HADRIAN'
(Other definitions for hadrian that I've seen before include "Roman emperor who visited Britain" , "His wall crosses northern Britain" , "Roman Emperor after Trajan" , "Wall-building Roman emperor" , "Imperial wall-builder" .)