the compound adjective 'wallet-sized' is a modern formation that follows a productive english pattern for specifying dimensions. the first element, 'wallet', originally referred to a bag for provisions, but its meaning narrowed to denote a small, flat case for holding money and cards. the second element, 'sized', derives from the noun 'size', which entered english from old french 'sise', originally meaning an allotted portion or regulation. the combination creates a transparent descriptor, literally meaning 'having the size of a wallet', used to indicate a compact, portable format, particularly for photographs or documents.

Structure: wallet (small flat case) + sized (having a size) 'wallet' (origin: late 14th century, from Anglo-French 'walet', a bag or knapsack, likely of Germanic origin; functional role: noun base denoting the object). 'sized' (origin: from the noun 'size' (dimensions) + the past participle suffix '-ed', from Old English '-ed'; functional role: adjective-forming suffix meaning 'having a specified size').