scarlet a brilliant red colour. The word comes (in Middle English, originally denoting any brightly coloured cloth) via Old French from medieval Latin scarlata, which in turn comes via Arabic and medieval Greek from late Latin sigillatus ‘decorated with small images’, from sigillum ‘small image’.
scarlet letter a representation of the letter A in scarlet cloth which persons convicted of adultery were condemned to wear, as described in the novel (1850) by Nathaniel Hawthorne, in which Hester Prynne, convicted of adultery in 17th-century New England, is sentenced to wear the scarlet letter on the breast of her gown for the rest of her life.
Scarlet Pimpernel the name assumed by Sir Percy Blakeney, the hero of a series of novels by Baroness Orczy (1865–1947), a dashing but elusive Englishman, hiding his true nature beneath a lazy and foppish exterior, who rescued potential victims of the French Reign of Terror; the scarlet pimpernel is the emblem which he often leaves behind to infuriate his baffled enemies.
scarlet woman an abusive epithet applied to the Roman Catholic Church, in allusion to Revelation 17:3–4, ‘And I saw a woman sit upon a scarlet coloured beast…And the woman was arrayed in purple and scarlet colour.’

See also an ape's an ape, a varlet's a varlet, though they be clad in silk or scarlet.

scar·let / ˈskärlit/ • adj. 1. of a brilliant red color: a mass of scarlet berries.2. chiefly dated (of an offense or sin) wicked; heinous. ∎  immoral, esp. promiscuous or unchaste.• n. a brilliant red color: papers lettered in scarlet and black. ∎  clothes or material of this color.

scarlet sb. †rich cloth, of various colours, freq. bright-red XIII; bright vivid red colour XV; adj. XIV. Aphetic — OF. escarlate fem. (mod. écarlate); of unkn. orig.