What does 'to be shut in' mean?

[dzungqn]

Test No. incompl/inter-10 "Close/Shut", question 7

After a number of years as a monk he decided to leave because he felt very ......... in.

(a) shut
(b) shutting
(c) closes
(d) closed

Test No. incompl/inter-10 "Close/Shut", answer 7

After a number of years as a monk he decided to leave because he felt very shut in.

Correct answer: (a) shut

Your answer was: correct
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please explain what "to be shut in" means

[Torsten]

to be shut in = to be isolated/secluded
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