One Charlie blocking Iberian city entrance (7)
I believe the answer is:
portico
'entrance' is the definition.
(thesaurus)
'one charlie blocking iberian city' is the wordplay.
'one' becomes 'i' (Roman numeral).
'charlie' becomes 'C' (phonetic alphabet).
'blocking' means one lot of letters goes inside another (block can mean to plug a gap in something).
'iberian city' becomes 'porto' (Portuguese city).
'i'+'c'='ic'
'ic' placed within 'porto' is 'PORTICO'.
(Other definitions for portico that I've seen before include "A number of columns" , "gallery, perhaps" , "Porch-like structure with columns" , "Classical porch" , "covered area" .)