Start to register web address blocked by one country (5)
I believe the answer is:
rural
'country' is the definition.
('rural' can be similar in meaning to 'country')
'start to register web address blocked by one' is the wordplay.
'start to' indicates taking the first letters.
'web address' becomes 'url' (I've seen this in other clues).
'blocked by' means one lot of letters goes inside another (I've seen this in other clues).
'one' becomes 'a'.
The initial letter of 'register' is 'r'.
'url' enclosing 'a' is 'ural'.
'r'+'ural'='RURAL'
(Other definitions for rural that I've seen before include "Countryfied" , "Characteristic of the countryside" , "living in the countryside" , "Arcadian" , "Agrestic" .)