'assignation' originates from Latin, specifically the Medieval Latin word 'assignatio' ultimately from 'assignare,' where the prefix 'ad-' (appearing as 'as-') meant 'to/toward' and 'signare' meant 'to mark or sign.'

'assignation' changed from Medieval Latin 'assignatio' into Old French/Anglo-Norman forms (e.g. 'asignacion'), then appeared in Middle English (e.g. 'assignacioun') and eventually became the modern English 'assignation'.

Initially, it meant 'the act of assigning or allotting,' but over time it came to include the sense 'a private appointment or rendezvous,' which is the common modern meaning.