Afloat in a boat (7)

I believe the answer is:

pontoon

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

'boat' is the definition.
(I know that pontoon is a type of barge)

I can't explain the rest of the clue.

(Other definitions for pontoon that I've seen before include "'Flat-bottomed boat, card game and Mayo town (7)'" , "Card game; floating support" , "Card-game" , "Card game - type of bridge" , "Half of 1D [GAME OR BIRD]" .)

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

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