Vagrant unsettled briefly among CID (7)
I believe the answer is:
nomadic
'vagrant' is the definition.
(I've seen this in another clue)
'unsettled briefly among cid' is the wordplay.
'unsettled' indicates an anagram.
'briefly' means to remove the last letter.
'among' with its final letter taken away is 'amon'.
'amon'+'cid'='amoncid'
'amoncid' with letters rearranged gives 'NOMADIC'.
(Other definitions for nomadic that I've seen before include "Lacking fixed home" , "Perhaps unsettling" , "Peripatetic" , "migrant" , "Unsettled" .)