Jealous chap announced takeover stake in company stock (9)
I believe the answer is:
greenmail
'takeover stake in company stock' is the definition.
I can't judge whether this defines the answer.
'jealous chap announced' is the wordplay.
'jealous' becomes 'green'.
'chap' becomes 'male' (chap can mean a man).
'announced' indicates a 'sounds like' (homophone) clue.
'male' sounds like 'mail'.
'green'+'mail'='GREENMAIL'
Can you help me to learn more?
(Another definition for greenmail that I've seen is " dubious business practice".)