Prefix with lingual or lateral

TRI

["Think of a number that often appears in terms describing three-part divisions, like in geometry or music."]

This clue is looking for a short word that goes before "lingual" or "lateral" to form common terms. "Tri" fits because it creates "trilingual" (speaking three languages) and "trilateral" (involving three sides or parties). The prefix "tri-" simply means "three," so the answer is straightforward once you spot the pattern.