Etymology From Middle English grouchen, variant of grucchen (“to complain, mumble, murmur”). See grutch.
1
A complaint, a grumble, a fit of ill-humor.
But today he had noticed from the moment he had got out of bed that something was amiss with the world. Either he was in the grip of some divine discontent due to the highly developed condition of his soul, or else he had a grouch.1919, P. G. Wodehouse, 'A Damsel in Distress', Herbert Jenkins, 1956, p 20
2
One who is grumpy or irritable.
I don't feel like hanging around with that grouch.