Place concealing large old deity (5)
I believe the answer is:
pluto
'deity' is the definition.
(Pluto is an example)
'place concealing large old' is the wordplay.
'place' becomes 'put' (synonyms).
'concealing' indicates putting letters inside.
'large' becomes 'L' (eg in clothes sizes).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'put' enclosing 'l' is 'plut'.
'plut'+'o'='PLUTO'
(Other definitions for pluto that I've seen before include "underworld boss" , "Outermost of the main planets" , "Planet furthest from the sun" , "Distant planet" , "Solar system body" .)