let bygones be bygones

adjective

1. past; gone by; earlier; former: The faded photograph brought memories of bygone days.

noun

2. Usually bygones. that which is past: Let’s not talk of bygones.

Idioms

3. let bygones be bygones, to decide to forget past disagreements; become reconciled: Let’s let bygones be bygones and be friends again.

adjective

1. (usually prenominal) past; former

noun

2. (often plural) a past occurrence
3. (often plural) an artefact, implement, etc, of former domestic or industrial use, now often collected for interest
4. let bygones be bygones to agree to forget past quarrels

adj.early 15c., from by (adv.) + gone. Cf. similar construction of aforesaid. As a noun from 1560s (see bygones). Let past offenses and problems stay in the past; don’t let them taint the present. What’s done is done; don’t worry about the past, especially past errors or grievances. For example, Bill and Tom shook hands and agreed to let bygones be bygones. [First half of 1600s]