A number possibly looking cross (3)
'a number' is the definition.
(ten is a kind of number)
'looking cross' is the wordplay.
I cannot really see how this works, but
'cross' could be 't' (shape) and 't' is present in the answer.
The remaining letters 'en' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'possibly' is the link.
Can you help me to learn more?
(Other definitions for ten that I've seen before include "Half a score", "How many", "Very young", "time", "Figure".)