Unintentional sort of invader gets temporary accommodation (11)
I believe the answer is:
inadvertent
'unintentional' is the definition.
(I've seen this before)
'sort of invader gets temporary accommodation' is the wordplay.
'sort of' indicates anagramming the letters.
'gets' means one lot of letters go next to another.
'temporary accommodation' becomes 'tent' (people stay in a tent temporarily).
'invader' with letters rearranged gives 'inadver'.
'inadver'+'tent'='INADVERTENT'
(Other definitions for inadvertent that I've seen before include "Unthinking" , "Unintentional" , "unguarded" , "Accidental" , "without meaning" .)