To make something look neater and more attractive, or to improve someone's appearance or behavior.
From 'smart' (Old English 'smeortan,' meaning 'to bite' or 'sting'), which evolved to mean 'sharp' and 'neat.' The verb form developed in the 17th century.
The British phrase 'smarten up' became especially popular after military culture emphasized that appearance and posture directly affect confidence and how others perceive you.
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