Chemical engineer defends right to telephone customers (9)
I believe the answer is:
clientele
'customers' is the definition.
(I've seen this before)
'chemical engineer defends right to telephone' is the wordplay.
'chemical engineer' becomes 'ce' (this could be a standard abbreviation which I don't know about).
'defends' means one lot of letters goes inside another.
'right' becomes 'lien' (I've seen this before).
'to telephone' becomes 'tel' (short for telephone).
'lien'+'tel'='lientel'
'ce' enclosing 'lientel' is 'CLIENTELE'.
Can you help me to learn more?
(Other definitions for clientele that I've seen before include "All one's customers" , "Patrons" , "Customers (of a shop)" , "Customers, collectively" , "Market" .)