Having grave consequences (6)

I believe the answer is:

deadly

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

'grave consequences' is the definition.
'deadly' can be an answer for 'grave' (thesaurus). I'm unsure of the 'consequences' bit.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for deadly that I've seen before include "Belladonna" , "Lethal, capable of causing fatality" , "sniper aspires to be" , "Lethal, could be fatal" , "Lethal, capable of causing fatal injury" .)

I've seen this clue in The Globe and Mail.

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