A nicety is a small, important detail that can make a large difference. The word is commonly misused to mean an appealing characteristic, but in fact a nicety may not be nice in that sense. For example, knowing which knife and fork to use for which food at a formal banquet is one of the niceties of formal etiquette, but most of us would agree that such rules are silly, not nice. The confusion arises because the word nice, on which nicety is based, has changed meaning over time. The Latin word it comes from meant foolish or silly, but in English, in different centuries nice has meant timid, then dainty, then precise, then pleasant. Some of the older meanings survive. A subtle difference between two things is still called a nice distinction.
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