Student Jack's room (3)

I believe the answer is:

lab

'room' is the definition.

'student jack's' is the wordplay.
'student' becomes 'l' (as in L-plates for learner drivers).
'jack' becomes 'ab' (both can mean a sailor).
'l'+'ab'='LAB'

(Other definitions for lab that I've seen before include "retriever" , "Socialist" , "Science workshop" , "Chemist's workroom" , "Experimental facility" .)

I've seen this clue in The Telegraph.

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