n. 流放,充军;放逐,被放逐者;流犯
vt. 放逐,流放;使背井离乡
Several etymologies are possible. It might be a derivative of a verb *ex-sulere 'to take out' to the root *selh- 'to take', cf. consul and consulere; hence exsul 'the one who is taken out'. It might belong to amb-ulare *-al- 'to walk', hence 'who walks out'. It might even belong to *helh-, the root of [Greek elauno] 'to drive': ex-ul 'who is driven out' [de Vaan, "Etymological Dictionary of Latin and the other Italic Languages"]