The process of discoloring or marking something, or in scientific contexts, applying dyes to specimens to make structures visible under microscopy.
From Old French 'desteindre' meaning 'to remove color', which paradoxically evolved through Middle English to mean 'to color' or 'to discolor'. The scientific usage developed in the 19th century as microscopy advanced and researchers needed ways to distinguish cellular structures.
The irony of 'staining' is that it originally meant to remove color, yet now primarily means to add unwanted color or, in science, to add very much wanted color! In biology, staining techniques like Gram staining have been crucial for identifying bacteria, turning the 'flaw' of staining into an essential diagnostic tool.
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