Eastern male, messenger casting first stone (7)
I believe the answer is:
emerald
'stone' is the definition.
(type of gemstone)
'eastern male messenger casting' is the wordplay.
'eastern' becomes 'eme' (I can't explain this - if you can you should give a lot more credence to this answer).
'male' becomes 'he' (he refers to a man).
'messenger' becomes 'herald' (herald is a kind of messenger).
'casting' suggests deleting specific letters (as in casting away).
'herald' with 'he' taken away is 'rald'.
'eme'+'rald'='EMERALD'
'first' is the link.
Can you help me to learn more?
(Other definitions for emerald that I've seen before include "Led mare (anag.)" , "Gem; type of moth" , "...re medal? (Anag)" , "Green gemstone" , "Small size of type, in printing" .)