City in siege no Acre (5)
I believe the answer is:
genoa
'city' is the definition.
(Genoa is an example)
'in siege no acre' is the wordplay.
'in' indicates a hidden word.
'GENOA' can be found hidden inside 'siege no acre'.
(Other definitions for genoa that I've seen before include "Seaport in northwestern Italy" , "Type of rich fruit cake" , "North Italian port" , "Italian city has no age, oddly" , "Italian city; sail" .)