What is another word for "fundamental"?

Roget's Thesaurus (1911) lists these synonyms for "fundamental": animal, area, base, baseboard, based, basement, basis, bilge, bottom, built, centerboard, dado, deck, dimensional, earth, flag, floor, foot, footing, form, foundation, four, geographical, ground, hardpan, hold, hoof, keel, mopboard, nadir, nethermost, object, pavement, paving, plinth, quad, quadrangle, quadrate, quadratic, quadrature.