(after a verb or adjective) one who (is) ... / (after a noun) person involved in ... / -er / -ist / (used after a number or 後|后[hou4] or 前[qian2] to refer to sth mentioned previously) / (used after a term, to mark a pause before defining the term) / (old) (used at the end of a command) / (old) this
to assign / to appoint / to take up a post / office / responsibility / to let / to allow / to give free rein to / no matter (how, what etc) / classifier for terms served in office, or for spouses, girlfriends etc (as in 前任男友)