Spot old feline is trapped by a big one (8)
I believe the answer is:
location
'spot' is the definition.
(I've seen this before)
'old feline is trapped by a big one' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'feline' becomes 'cat' (cat is a kind of feline).
'is trapped by' is an insertion indicator.
'a big one' becomes 'lion' (I can't justify this - if you can you should give a lot more credence to this answer).
'o'+'cat'='ocat'
'ocat' inserted into 'lion' is 'LOCATION'.
(Other definitions for location that I've seen before include "Position or situation" , "Place, site" , "Whereabouts, position" , "Spot - where films may be shot" , "Position, point in space" .)