National firm once caught importing large antelope (9)
I believe the answer is:
icelandic
'national' is the definition.
Both the definition and answer are adjectives. Maybe there's an association between them I don't understand?
'firm once caught importing large antelope' is the wordplay.
'firm once' becomes 'ici' (I can't explain this - if you can you should give a lot more credence to this answer).
'caught' becomes 'c' (cricket abbreviation).
'importing' means one lot of letters goes inside another.
'large antelope' becomes 'eland' (large African antelope).
'ici'+'c'='icic'
'icic' placed around 'eland' is 'ICELANDIC'.
Can you help me to learn more?
(Other definitions for icelandic that I've seen before include "Like many sagas" , "in island republic" , "Eg, native to Reykjavik" , "Language of people of Reykjavik" , "As European" .)