Meaning/Usage: To agree to participate in the plan
Explanation: "Down" comes from "down to earth." When you are down to earth, you are realistic and not imagining things. Therefore, when you are "down," you are basically legitimate or a real. This is an informal way of saying you are in for the plan.
"If you don't want to go to the pool, I'll be down for whatever."
"I'll be down with whatever you guys want to do tonight."
"Going to the movies sounds good, I'm down."
A. "Just wanted to let you know we all might go skating tonight."
B. "I'm down. Sounds like fun to me."
A. "Ok then, we will pick you up around 7 o'clock."
B. "Sounds good."
Other Common Sentences
"I'm in."
"I agree with that."