In this state, a number cannot get the whole way! (4)
I believe the answer is:
iowa
'in this state a number cannot get the whole way' is the definition.
'iowa' can be an answer for 'state' (Iowa is an example). I am not certain of the remainder of the definition.
'in this state a number' is the wordplay.
'in' means one lot of letters goes inside another.
'this state' becomes 'IA'.
'a number' becomes 'ow' (I can't explain this - if you can you should give a lot more credence to this answer).
'ia' placed around 'ow' is 'IOWA'.
Can you help me to learn more?
(Other definitions for iowa that I've seen before include "'Hawkeye State'" , "American state, capital Des Moines" , "US state, three vowels" , "State of USA" , "part of United States" .)