Ring the gentleman from the jeweller’s (4)
I believe the answer is:
opal
'the jeweller's' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'ring the gentleman' is the wordplay.
'ring' becomes 'O' (letter resembling a ring).
'the gentleman' becomes 'pal' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'o'+'pal'='OPAL'
'from' acts as a link.
Can you help me to learn more?
(Other definitions for opal that I've seen before include "Precious stone" , "Something milky-white" , "Translucent gem" , "what may be set in 29 [DIAL]" , "Opaque gem" .)