ˈtrīˌfid, -_fə̇d adjective
Etymology: Latin trifidus split into three, from tri- + -fidus (from stem of findere to split) — more at bite
1. : divided partway to the base into three lobes with narrow sinuses : trident
2. of a cipher alphabet : constructed by matching the letters of the alphabet with 3-unit equivalents of such a nature that exactly as many of them can be constructed as there are letters of the alphabet (as by using the twenty-seven 3-digit numbers made up of one or more of the numerals 1, 2, and 3 for a 27-letter alphabet) — compare fractional substitution