Host finally cut off very vacuous swimmer (7)

I believe the answer is:

anchovy

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

'swimmer' is the definition.
(anchovy is a kind of aquatic vertebrate)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for anchovy that I've seen before include "Salty little fish" , "Small, salty-tasting fish" , "Small fish of herring family, nice on toast" , "Brit often found pickled" , "Small edible fish" .)

I've seen this clue in The Times and The Sunday Times.

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