Someone cheerful is happy in a way you can see and hear. The neighbour who says good morning and means it, a nurse who is cheerful at six in the morning, whistling from the next room while the kettle goes on.
It works on places and things as well as people: a cheerful yellow kitchen, a cheerful little café, a cheerful fire in the grate — anything that lifts the mood of a room. There is a second use about facing trouble without complaint: cheerful about the diagnosis, cheerful in the rain, cheerful while the whole thing falls apart. Cheerfully is the adverb and cheerfulness the noun. The near neighbours all sit slightly differently: cheery is lighter and brisker, jolly is louder and rounder, merry means Christmas or drink. One L in cheerful, two in cheerfully.
1adjectivecheerfulHappy, and showing it in your face and voice.
“He gave a cheerful wave from the far side of the road.”
2adjectivebrightBright and pleasant, of a place or thing.
“They painted the hallway a cheerful yellow.”
3adjectivefacingFacing difficulty without complaining.
“She stayed cheerful through six weeks of rain and a broken boiler.”
Too few real examples of this word to estimate which sense is commonest.
Cheerful is one of the plainest builds in English: cheer plus -ful, put together in Middle English as chereful. Full of cheer, and that is still exactly what it means. The seam has not moved in six hundred years.
Middle English
chereful
English, today
cheerful
From Middle English chereful, cherful, equivalent to cheer + ful.
Etymology from Wiktionary, CC BY-SA