the term is a modern english compound noun, later used attributively as an adjective. the first element, 'wallet', originally referred to a traveler's bag, but its meaning narrowed to denote a small, flat case for carrying money and cards. the second element, 'size', derives from a legal term for an ordinance fixing a standard, which evolved to mean dimensions. combined, 'wallet-size' literally means 'having the dimensions of a wallet', a specification that became standardized for small, portable photographs, linking the object's physical scale to a common personal item for easy carrying.

Structure: wallet (small flat case) + size (dimensions) - wallet: from middle english 'walet', meaning 'bag, knapsack', of germanic origin, likely from old french 'walet'. functions as a noun used attributively to specify the type. - size: from old french 'sise', a shortening of 'assise', meaning 'ordinance, act of fixing', ultimately from latin 'assidere' (to sit beside, assist in office). functions as a noun indicating dimensions or magnitude.