Celestial as river in short story (6)
I believe the answer is:
astral
'celestial' is the definition.
(I've seen this in another clue)
'as river in short story' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'in' means one lot of letters goes inside another.
'short' means to remove the last letter.
'story' becomes 'tale' (synonyms).
'tale' with its final letter removed is 'tal'.
'r' put within 'tal' is 'tral'.
'as'+'tral'='ASTRAL'
(Other definitions for astral that I've seen before include "Related to the stars" , "Resembling the stars - of the spirit world" , "Starry sort of altars." , "19 [STELLAR]" , "To do with stars on altars" .)