the.com/curmudgeon

means A gruff, often older person who is quick to grumble and resistant to cheerfulness or sentiment, though frequently softer underneath than they let on.

from One of the great mystery words of English — it appeared in the 1500s and its roots are genuinely unknown. Samuel Johnson's dictionary famously claimed it came from French 'coeur mechant' ('evil heart'), but that was a guess dressed up as fact, and it's now considered a folk etymology rather than true history. No one has ever traced it convincingly to any source — curmudgeon simply grumbled its way into the language and stayed.