In which the beast of Siberia is caught? (5)
I believe the answer is:
taiga
'in' is the definition.
Both the definition and answer are singular nouns.
Perhaps there's an association between them I don't understand?
'the beast of siberia is caught?' is the wordplay.
'the beast of siberia' becomes 'tiger'.
'is caught?' indicates a 'sounds like' (homophone) clue (I've seen 'is caught' mean this).
'tiger' is a homophone of 'TAIGA'.
'which' acts as a link.
(Other definitions for taiga that I've seen before include "Siberian subarctic forest(s)" , "trees" , "Marshy pine forest" , "coniferous forests" , "Boggy forest" .)