Crossword Genius

An outright kill to sustain a hungry whale (5)

Ross

I believe the answer is:

krill

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

'whale' is the definition.
The definition and answer can be both animals as well as being singular nouns.
Maybe they are linked in a way I don't understand?

I can't explain the remainder of the clue.

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(Other definitions for krill that I've seen before include "Tiny shrimps" , "Tiny crustaceans" , "Food of whalebone whales" , "Whale food" , "Crustaceans eaten by whales" .)

I've seen this clue in the Evening Standard.
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