Inclined to grumble; having the quality or habit of complaining in a petulant manner.
Formed from grumble plus the -some suffix, which creates adjectives meaning 'having the quality of' (like tiresome, lonesome). This is a somewhat archaic or playful formation.
The -some suffix is fascinating because it creates adjectives that sound almost affectionate when describing annoying things—'grumblesome' feels almost endearing, like you're gently poking fun at the person rather than condemning them.
Complete word intelligence in one call. Free tier — 50 lookups/day.