Fat lady in a rowing boat? (5)

I believe the answer is:

eight

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

'rowing boat?' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for eight that I've seen before include "Number (of oarsmen?)" , "Half a quarter" , "One over this for drunkeness" , "A number, sounds like swallowed" , "4x2" .)

I've seen this clue in the Evening Standard.

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