1911 Encyclopædia Britannica/Carpet-knight

CARPET-KNIGHT, properly one who has been knighted in time of peace on the carpet before the king’s throne, and not on the field of battle as an immediate reward for valour. It is used as a term of reproach for a soldier who stays at home, and avoids active service and its hardships, with a particular reference to the carpet of a lady’s chamber, in which such a sainéant soldier lingers.