merry

Base information:

• Denotation: "pleasing, agreeable, pleasant, sweet, exciting feelings of enjoyment and gladness"
• Root: myrge
• Root Language: Old English
• Type: free
• Etymonline Root Search
• Etymonline Base Page
• Wiktionary Base Page
• Wiktionary Root Page

Word sums:

• Merry + ness -> merriness
• Merry + est -> merriest
• Merry + er -> merrier
• Merry + Thought -> merrythought
• Merry + Make + ing -> merrymaking
• Merry + ment -> merriment
• Merry + ly -> merrily