Number clever enough for game show (7)
I believe the answer is:
Here is my best explanation:
'game show' is the definition.
(UK game show)
'number clever enough' is the wordplay.
'number' becomes 'ten' (ten is a kind of number**).
'clever enough' becomes 'able'.
'for' is the link.
(Other definitions for tenable that I've seen before include "Based on sound reasoning or evidence", "Viable", "Able to be believed", "Can be maintained", "Able to be held", "Able to be defended against attack or objection", "Believable", "Well-founded", "Can be defended" and "Capable of being kept".)