Synonyms:
- backside,
- base,
- basement,
- basis,
- beam,
- bearing wall,
- bed,
- bedding,
- bedrock,
- behind,
- belly,
- bottom,
- bottom side,
- breech,
- buttocks,
- derriere,
- downside,
- floor,
- flooring,
- fond,
- footing,
- foundation,
- fundamental,
- ground,
- grounds,
- groundwork,
- hardpan,
- lower side,
- lowest layer,
- lowest level,
- nether side,
- nethermost level,
- pavement,
- posterior,
- principle,
- radical,
- rear,
- riprap,
- rock bottom,
- rudiment,
- rump,
- seat,
- sill,
- solid ground,
- solid rock,
- stereobate,
- stylobate,
- substratum,
- substruction,
- substructure,
- terra firma,
- underbelly,
- underbuilding,
- undercarriage,
- undergirding,
- underlayer,
- underneath,
- underpinning,
- underside,
- understruction,
- understructure