The first derivative is the rate of change, and the second derivative is the rate of change of the rate of change.
delicious scrunptious is slang meaning delightful or first-rate.
Boss
The likely word is "primo" (chief part of a duet, or slang meaning superb, first-rate).
Applying the standard or going rate
Bradycardia is the medical term meaning abnormally low heart rate.
3
To rate or chide vehemently; to scold.
The value of something
You have a heart. It beats periodically. The rate at which it does so is your heart rate. If you don't have a heart rate, then your heart isn't beating, meaning you're dead or dying.
Chemical equilibria are dynamic, meaning the forward rate and reverse rate are equal.
The rate of change of velocity, either increasing or decreasing, is its acceleration or deceleration.