Arab leader always imprisoning me (5)
I believe the answer is:
emeer
'arab leader' is the definition.
(historical title in Islamic countries)
'always imprisoning me' is the wordplay.
'always' becomes 'eer' (poetic way of saying ever).
'imprisoning' means one lot of letters goes inside another.
'eer' enclosing 'me' is 'EMEER'.
(Other definitions for emeer that I've seen before include "independent ruler" , "Arabic title" , "Islamic title" , "Prince" , "Meryl -, US actress" .)