pardonable (adj.)

mid-15c., pardounen, "to forgive for offense or sin," from Old French pardoner and Medieval Latin perdonare (see pardon (n.)).

'I grant you pardon,' said Louis XV to Charolais, who, to divert himself, had just killed a man; 'but I also pardon whoever will kill you.' [Marquis de Sade, "Philosophy in the Bedroom"]

Related: Pardoned; pardoning. Pardon me as a phrase used when making apology is by 1764; pardon my French as exclamation of apology for obscene language is by 1895.

1520s, from un- (1) "not" + pardonable (adj.). Related: Unpardonably. Impardonable also is from 1520s.