Comparative form of cheerful; more full of cheer and happiness than something else.
From 'cheerful' (full of cheer) plus the comparative suffix '-er.' Though 'more cheerful' is now standard, older English and some dialects still use '-er' for this multi-syllable adjective.
English is messily inconsistent with its comparatives—we say 'happier' but 'more beautiful,' and 'cheerfuller' sounds archaic now even though it follows perfectly logical grammar rules that our language used to prefer.
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