Old King Cole's string trio? (5)
I believe the answer is:
three
'trio?' is the definition.
(I know that 3 can be written as three)
'old king cole's string' is the wordplay.
I cannot quite understand how this works, but
'king' could be 'r' (abbreviation for rex, king in Latin) and 'r' is found in the answer.
The remaining letters 'thee' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for three that I've seen before include "Amount in a trio" , "Number of Dumas's musketeers" , "One, one, one" , "Start to count back, briefly" , "So many 12s today" .)