With all the purported 'engineers' here, I am amazed that no one has referenced the AES (Audio Engineering Society) - a 75 year old standards organization - for definitions.
From the compressor entry:
"A signal processing device used to reduce the dynamic range of the signal passing through it."
Makeup gain is not required to have a compressor circuit/process; it is a utility add-on that makes it easier to use in certain cases.
https://www.aes.org/par/c/