bedrock

noun

1. Geology. unbroken solid rock, overlaid in most places by soil or rock fragments.
2. bottom layer; lowest stratum.
3. any firm foundation or basis: Technical courses will be founded on a bedrock of sound, general education so as to produce a well-rounded engineer.
4. the fundamental principles, as of a teaching, belief, or science: Let’s strip away the cant and get down to bedrock.

adjective

5. basic; fundamental.

noun

1. the solid unweathered rock that lies beneath the loose surface deposits of soil, alluvium, etc
2. basic principles or facts (esp in the phrase get down to bedrock)
3. the lowest point, level, or layer

n.

also bed-rock, 1850, from bed (n.) + rock (n.). Figurative use by 1869; as an adjective by 1881.

1. The solid rock that lies beneath the soil and other loose material on the Earth’s surface.