Wavering, undulating, or tending to flow; in medicine, describing a swelling that moves or ripples when pressed.
From Latin 'fluctuans' (flowing, undulating), present participle of 'fluctuare' (to wave or flow). The medical meaning developed when doctors needed to describe certain types of swellings that respond to pressure.
In medicine, a fluctuant mass means there's fluid inside that moves around—doctors use this when diagnosing cysts or abscesses. It's one of those Latin words that doctors kept because it's precise and sounds professional.
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