grump /ɡɹʌmp/noun 2verb 2forms 3 noun2 •(informal) A habitually grumpy or complaining person. •(informal) A grumpy mood.If you're not taking Action to change the situation, either sit in a grump or Accept it. — 2004 verb2 •(informal) To complain.But Murial Jane was now in a grumping mood[.] — 1936 •(informal) To be grumpy. formsgrumped · grumping · grumps