Cover small taxi off across river (8)
I believe the answer is:
scabbard
'cover' is the definition.
(cover for a sword)
'small taxi off across river' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'taxi' becomes 'cab' (synonyms).
'off' becomes 'bad' (I've seen this in other clues).
'across' means one lot of letters goes inside another.
'river' becomes 'r' (abbreviation for river).
'bad' enclosing 'r' is 'bard'.
's'+'cab'+'bard'='SCABBARD'
(Other definitions for scabbard that I've seen before include "Weapon held here" , "sword-carrier" , "place of weapon" , "Sheath for sword or dagger" , "It keeps food off clothes" .)