bedrock
1.
n. fundamentals; solid facts.
Let's get down to bedrock and quit wasting time.This is bedrock—the truth.
2.
mod. fundamental.
You've been avoiding the bedrock issues all your life.Let's hear some more about these bedrock ideas.
gut
mod. basic; fundamental.This is a gut issue, and we have to deal with it now.We are not dealing with what I would call one of the gut matters of the day.
nuts and bolts
n. the mundane workings of something; the basics of something.I want you to learn how to write well. You have to get down to the nuts and bolts of writing.She's got a lot of good, general ideas, but when it comes to the nuts and bolts of getting something done, she's no good.