Catch sight of small earthenware vessel (4)
I believe the answer is:
spot
'catch sight of' is the definition.
(spotting is a kind of catching sight of)
'small earthenware vessel' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'earthenware vessel' becomes 'pot'.
's'+'pot'='SPOT'
(Other definitions for spot that I've seen before include "station" , "Observe - locality" , "Espy; mark" , "Notice; sign of acne" , "See; round mark" .)