Tall, thin layabout finishes drink (5)
I believe the answer is:
lanky
'tall' is the definition.
(similar in meaning)
'thin layabout finishes drink' is the wordplay.
I cannot quite understand how this works, but
'thin' could be 'lank' (similar in meaning) and 'lank' is found within the answer.
A single letter 'y' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for lanky that I've seen before include "Inelegantly tall and thin" , "Awkwardly tall" , "Bony" , "Far from podgy" , "Tall and gangling" .)