Menace from Teheran dissipated after time (8)
I believe the answer is:
threaten
'menace' is the definition.
('threaten' can be a synonym of 'menace')
'teheran dissipated after time' is the wordplay.
'dissipated' indicates anagramming the letters.
'after' means one lot of letters go next to another.
'time' becomes 't'.
'teheran' with letters rearranged gives 'hreaten'.
'hreaten' put after 't' is 'THREATEN'.
'from' acts as a link.
(Other definitions for threaten that I've seen before include "Utter menaces" , "State an intention to harm" , "Foreshadow" , "Menace - impend" , "indicate danger" .)