Heteronym
Two (or more) words or phrases with the same spelling are used with different meanings. Examples: tarry (“to linger”), tarry (“covered with tar”); Mount St. Helens, mounts the lens; mustache, must ache. Unlike most flats, heteronyms need not have bases that have dictionary nature—in fact, long, contrived phrases are welcome as long as they are well clued in the verse. We require that the different portions not overlap etymologically, although exceptions are often made for short words (e.g., “the”) or common morphemes (e.g., “-ing”).
A base in which sounds, letters, and spacing remain unchanged, as in bear (carry) and bear (ursine), is still a heteronym, but the restriction on shared etymology makes these rare.
“Heteronymic” also refers to changes in word breaks, even if pronunciation doesn’t change: cargo, car go. Examples may be found in cryptic clueing, picture puzzles, and the heteronymy of a rebus’s reading and answer.
A reversed heteronym is a mynoreteh. A phonetic heteronym is a homonym.