One very quiet in US city, being chilly (5)
I believe the answer is:
nippy
'being chilly' is the definition.
(thesaurus)
'one very quiet in us city' is the wordplay.
'one' becomes 'i' (Roman numeral**).
'very quiet' becomes 'pp'.
'in' means one lot of letters goes inside another.
'us city' becomes 'ny' (I've seen this in other clues).
'i'+'pp'='ipp'
'ipp' put inside 'ny' is 'NIPPY'.
(Other definitions for nippy that I've seen before include "Very cold - quick (informal)" , "Quick; chilly" , "Speedy - cold" , "Sharp" , "Fast - cold" .)