Siberian spooks cutting City Hall line (7)
I believe the answer is:
glacial
'siberian' is the definition.
(thesaurus)
'spooks cutting city hall line' is the wordplay.
I cannot really understand how this works, but
'spooks' could be 'cia' (spooks can mean spies) and 'cia' is present in the answer.
'city' could be 'la' (Los Angeles) and 'la' is present in the answer.
'line' could be 'l' (used when specifying particular lines from a poem) and 'l' is located in the answer.
A single letter 'g' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for glacial that I've seen before include "Cold and icy" , "Pertaining to the ice ages" , "Of slow moving ice masses" , "Ice cold" , "Frigid" .)