嫡

adjective: of the legal/primary wife (as opposed to a concubine's); of direct/lineal descent; orthodox, legitimate
嫡

diah4 (vernacular) and dêg4 (literary) are a register pair for the same word, not competing senses. The page's Chinese-section entry lists five related senses ("primary wife," "of/by the legal wife," short for 嫡子, "of lineal descent," "orthodox/authentic"), condensed here into one adjectival gloss covering the common modifier usage (嫡子, 嫡系, 嫡親); the staged cache had recorded this headword as a bare stub with no senses at all.