To make cheerful or to cause something to become bright and joyful.
From 'cheerful' (full of cheer and happiness) plus the suffix '-ize' meaning 'to make or become.' This is a relatively modern construction using productive English word-building patterns.
The suffix '-ize' is incredibly productive in English—we keep creating new verbs this way (like 'prioritize' or 'weaponize'), showing how languages evolve by recycling existing pieces rather than inventing entirely new words.
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