(n.) That which forms the foundation or support of anything; the basis; the essential or fundamental part; first principle.

arrangement base basement basic training basis bearing wall bed bedding bedrock bottom briefing clearing the decks cornerstone equipment familiarization fixing floor flooring fond footing foundation fundament fundamental ground grounds hardpan infrastructure makeready making ready manufacture mobilization pavement planning prearrangement preliminaries preliminary preliminary act preliminary step prep preparation preparatory study preparing prepping prerequisite pretreatment principle processing propaedeutic provision radical readying riprap rock bottom root rudiment seat sill solid ground solid rock spadework stereobate stylobate substratum substruction substructure terra firma training treatment trial tryout underbuilding undercarriage undergirding underpinning underpinnings understruction understructure warm-up