Huge profit monarch invests poorly (7)

I believe the answer is:

killing

I'm a little stuck... Click here to teach me more about this clue!

'huge profit' is the definition.
'killing' can be an answer for 'profit' (thesaurus). I am unsure of the 'huge' bit.

'monarch invests poorly' is the wordplay.
'monarch' becomes 'king' (king is a kind of monarch).
'invests' is an insertion indicator (inserted letters are invested).
'poorly' becomes 'ill' (synonyms).
'king' enclosing 'ill' is 'KILLING'.

Can you help me to learn more?

(Other definitions for killing that I've seen before include "Slaughtering" , "Terminating a life" , "Fortune" , "Slaughter" , "Murdering" .)

I've seen this clue in The Telegraph.

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