the compound adjective 'thigh-length' is a modern english formation, combining two native germanic elements. the first element, 'thigh', descends from old english 'þēoh', a word of ancient germanic lineage referring specifically to the upper leg. the second element, 'length', originates from old english 'lengþu', an abstract noun formed from the adjective 'long', which itself traces back to the proto-germanic 'langgaz'. the compound's logic is transparently descriptive, directly stating the measurement ('length') of a garment relative to a specific body part ('thigh'). this pattern of [body part] + 'length' is a productive method in english for specifying clothing dimensions, creating a clear, functional term for fashion and design.

Structure: thigh (body part) + length (measurement) thigh: from old english 'þēoh', of germanic origin, referring to the part of the leg between the hip and the knee. it functions as the noun base specifying the location. length: from old english 'lengþu', derived from the germanic root of 'long'. it functions as a noun suffix indicating the extent or measurement of something.