Once ordered ice cream (4)
I believe the answer is:
cone
'ice cream' is the definition.
(cone can refer to an ice cream cone)
'once ordered' is the wordplay.
'ordered' indicates anagramming the letters.
'once' anagrammed gives 'CONE'.
(Other definitions for cone that I've seen before include "Solid figure" , "often full of ice" , "Movable plastic bollard" , "Shape, the base is a circle and the sides taper up to a point" , "Geometrical shape" .)