Endlessly make point holding old spear (7)
I believe the answer is:
harpoon
'spear' is the definition.
(synonyms)
'endlessly make point holding old' is the wordplay.
'endlessly make point' becomes 'harp on' (to harp on is to make a point repeatedly).
'holding' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'harpon' going around 'o' is 'HARPOON'.
(Other definitions for harpoon that I've seen before include "Whale-hunting spear" , "Spear with a line attached for fishing" , "Spear for old whaler" , "Whaler's weapon" , "word often used in Moby-Dick" .)