Former leader in Tehran has worked hard (4)
I believe the answer is:
shah
'former leader in tehran' is the definition.
I can't judge whether this definition defines the answer.
'has worked hard' is the wordplay.
'worked' indicates an anagram.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'has' anagrammed gives 'sha'.
'sha'+'h'='SHAH'
Can you help me to learn more?
(Other definitions for shah that I've seen before include "Former Persian ruler" , "Old Middle Eastern ruler" , "Persian emperor" , "Iranian emperor" , "Former hereditary monarch of Iran" .)