True alarm spreading about unknown non-resident (10)
I believe the answer is:
extramural
'non-resident' is the definition.
I can't tell whether this defines the answer.
'true alarm spreading about unknown' is the wordplay.
'spreading' indicates an anagram.
'about' indicates putting letters inside.
'unknown' becomes 'x' (algebra).
'true'+'alarm'='truealarm'
'truealarm' is an anagram of 'etramural'.
'etramural' enclosing 'x' is 'EXTRAMURAL'.
Can you help me to learn more?
(Other definitions for extramural that I've seen before include "outside city limits" , "Not on course" , "What may be a wide painting" , "outside city walls" , "Taking place off campus?" .)