Small ice cream or cake (5)
I believe the answer is:
scone
'cake' is the definition.
(scone is a type of cake)
'small ice cream' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'ice cream' becomes 'cone' (cone can refer to an ice cream cone).
's'+'cone'='SCONE'
'or' acts as a link.
(Other definitions for scone that I've seen before include "Plain cake (for Scottish kings?)" , "Griddle-cake" , "Tea-time treat" , "Savoury cake" , "Plain teatime cake" .)