Height 110 around capital city (6)
I believe the answer is:
climax
'height' is the definition.
(thesaurus)
'110 around capital city' is the wordplay.
'110' becomes 'CX' (roman numerals).
'around' means one lot of letters goes inside another.
'capital city' becomes 'lima' (capital of Peru).
'cx' placed around 'lima' is 'CLIMAX'.
(Other definitions for climax that I've seen before include "Culminating moment" , "Highest point" , "exciting finale" , "Crux, turning point" , "High point" .)