Dis-ing

There's "enchanted," and "disenchanted."

I understand "agreeable" and "disagreeable."

I know what it means to be "disengaged" after having an engaging experience.

"Associated" - "disassociated."

I even acknowledge "proportionate" and "disproportionate," because they make sense.

But can anyone tell me...what is it to be "gruntled" in order to become "disgruntled"? How do you achieve a state of gruntleness from which to become disgruntled?

Anyone?