The word "wedgie" is a modern, informal American English formation from the mid-20th century. It is a straightforward compound noun built directly from the existing English word "wedge," which descends from the Old English wecg, a term for a solid, V-shaped object. The addition of the diminutive "-ie" suffix transforms the concrete concept of a wedge into a slang term for a specific, juvenile prank, humorously likening the resultant underwear configuration to the shape of a wedge being forced into a crevice. Its secondary meaning for a wedge-heeled shoe follows the same logical pattern, applying the suffix to a fashion item characterized by its wedge shape.

Structure: wedg (wedge) + ie (diminutive/informal noun suffix) - wedg: From the English word "wedge," of Old English origin (wecg), meaning a piece of material thick at one end and tapering to a thin edge. In this compound, it conveys the core action and shape of the prank. - ie: A common English suffix used to form informal or diminutive nouns (e.g., doggie, movie). It indicates the word refers to a specific, often trivial or humorous, instance or item.