1. (a.) Basic, elemental; serving for the foundation; essential; elementary; as, a fundamental truth; a fundamental axiom\.

2. (n.) A leading or primary principle, rule, law, or article, which serves as the groundwork of a system; essential part, as, the fundamentals of the Christian faith.

AF ab ovo abecedarian aboriginal antenatal audio frequency austere autochthonous axiom bare basal base basement basic basilar basis bearing wall bed bedding bedrock beginning bench mark bottom budding cardinal cardinal point center central chaste chief thing climax component constituent constitutional constitutive core cornerstone creative crisis critical critical point crucial crux dominant element elemental elementary elements elixir embryonic essence essential essential matter factor fetal first floor flooring flower focal focus fond footing formative foundation foundational frequency fundament fundamental tone generative genetic germinal gestatory gist grammar gravamen great point ground grounds groundwork gut hardpan harmonic heart high point homely homespun homogeneous hypostasis important important thing in embryo in its infancy in ovo in the bud inaugural inceptive inchoate inchoative incipient incunabular indispensable indivisible infant infantile inherent initial initiative initiatory inner essence intonation intrinsic introductory inventive irreducible issue kernel keystone landmark law life-and-death life-or-death main main point main thing marrow material material point meat mere milestone monolithic monotone monotony nascent natal necessary needful nub nucleus nuts and bolts of a piece of the essence of vital importance organic original overtone paramount part and parcel partial partial tone parturient pavement pitch pith pivot plain postnatal postulate pregnant prenatal primal primary prime primeval primitive primogenial primordial principal principium principle principles pristine procreative protogenic pure pure and simple quid quiddity quintessence quintessential radical real issue requisite riprap rock bottom rudiment rudimental rudimentary rudiments rule salient point sap seat seminal severe sill simon-pure simple sine qua non single solid ground solid rock soul spare spirit stark stereobate stuff stylobate substance substantial substantive substantive point substratum substruction substructure terra firma the bottom line the nitty-gritty the point theorem tone tonelessness turning point unadorned uncluttered underbuilding undercarriage undergirding underlying underpinning understruction understructure undifferenced undifferentiated uniform ur vital