rare: Rare ‘uncommon’ [15] and rare ‘underdone’ [17] are not the same word. The former was borrowed from Latin rārus, which originally signified ‘having a loose texture, widely separated’ – hence ‘scarce’. It is not known what its ultimate source is. The latter is an alteration of the now obsolete rear ‘underdone’ (originally used mainly of eggs: ‘They had at their dinner rear eggs’, Book of the knight of the tower 1450), which goes back to Old English hrēr – again of unknown origin. [rare etymology, rare origin, 英语词源]