Good story about a very old urn, abridged (10)
I believe the answer is:
favourable
'good' is the definition.
('favourable' is associated in meaning with 'good')
'story about a very old urn abridged' is the wordplay.
'story' becomes 'fable' (fable is a kind of story**).
'about' indicates putting letters inside.
'very' becomes 'v' (abbreviation).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'abridged' means to remove the last letter.
'a'+'v'+'o'+'urn'='avourn'
'avourn' with its final letter taken away is 'avour'.
'fable' going around 'avour' is 'FAVOURABLE'.
(Other definitions for favourable that I've seen before include "20 [GOOD]" , "Propitious" .)