The Mohammedan world is hit (5)
I believe the answer is:
islam
'the mohammedan world' is the definition.
The answer and definition can be both groups as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'is hit' is the wordplay.
'hit' becomes 'lam' (to 'lam' means to hit hard).
'is'+'lam'='ISLAM'
Can you help me to learn more?
(Other definitions for islam that I've seen before include "Mails to great eastern religion" , "Religion of the Koran" , "Faith with five pillars" , "Mohammed's religion" , "Religion based on Muhammad's teachings" .)