IPA: /ˈɡrʌm.pi.ər/
KK: /ˈɡrʌm.pi.ɚ/
More irritable or bad-tempered than someone or something else.
After a long day at work, he felt grumpier than usual.
Comparative: grumpier
Superlative: grumpiest
Grumpier is formed from "grump" (of uncertain origin, possibly imitative of a grumbling sound) and the suffix "-ier" (meaning more). The word "grumpier" means more grumpy or irritable than usual.
Think of someone who is making a grumbling sound, which helps you remember that 'grumpier' means more irritable or grumpy.