Clear web sites centrally (4)
I believe the answer is:
nett
'clear' is the definition.
(similar in meaning)
'web sites centrally' is the wordplay.
'web' becomes 'net' (synonyms).
'centrally' says to take the centre.
The middle letter of 'sites' is 't'.
'net'+'t'='NETT'
(Other definitions for nett that I've seen before include "not including packaging" , "cleared of all charges" , "Pay" , "Free of tax" , "Opposite of gross" .)