Little old gentleman is a god (6)
I believe the answer is:
osiris
'god' is the definition.
(Egyptian god)
'little old gentleman is a' is the wordplay.
'little' means to remove the last letter (the word is not quite complete).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'gentleman' becomes 'sir' (a man may be addressed as sir).
'o'+'sir'+'is'+'a'='osirisa'
'osirisa' with its final letter taken away is 'OSIRIS'.
(Other definitions for osiris that I've seen before include "Husband of Isis, father of Horus - sis or I (anag)" , "Egypt. god of dead" , "God, husband of Isis" , "one held to be divine" , "once highly esteemed by Egyptians" .)