I’m getting stuck into beer vessel without end (7)

I believe the answer is:

aimless

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But I can't explain it at all! Could you help me understand?

(Other definitions for aimless that I've seen before include "Without purpose or direction" , "Without purpose, like Melissa" , "Without objectives" , "Rambling" , "Without purpose or plan" .)

I've seen this clue in The Times.

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