'scalloped-legged' originates from Modern English as a compound of 'scalloped' and 'legged'. 'Scalloped' itself comes (via Middle English) from Old French 'escalope' / Late Latin 'scallopa', where the root referred to a 'shell' or 'cup' and came to describe edges like a scallop shell; 'legged' derives from Old English 'leg', meaning 'limb'.

'scalloped' changed from Old French 'escalope' to Middle English 'scallop' and then to the adjective 'scalloped' meaning 'having scallop-like edges'; 'leg' from Old English remained in use and formed the past-participle-based compound '-legged' to mean 'having legs' or 'with legs of a specified form', producing Modern English compounds like 'scalloped-legged'.

Initially, the root for 'scallop' referred to a shell or cup; over time it came to describe an edge shaped like that shell (i.e., a series of rounded projections). 'Scalloped-legged' developed in modern usage to describe legs (of furniture, garments, etc.) that bear that scalloped shape.