fundamental; essential (pertaining to the basic part or notion of something)

Superseded spelling of interação fundamental. (Superseded in Brazil by the 1943 spelling reform and by the Portuguese Language Orthographic Agreement of 1990 elsewhere. Still used in countries where the agreement hasn’t come into effect.)

(physics) fundamental interaction

(Brazil, education) elementary school, primary school

(religion) fundamentalism

fundamentalist (one who reduces religion to strict interpretation of core or original texts)

fundamentally

plural of fundamentalista