To make or become dense; an archaic or dialectal form meaning to increase in density or thickness.
From dense + -en (archaic suffix forming verbs). This is a very old English form that's mostly obsolete now, replaced by more modern verbs like 'densify' or simply 'compress.'
Old English loved verbs formed with -en (like 'darken' or 'widen'), and 'densen' follows that pattern—it's poetic but obsolete, which is why you'll only spot it in historical texts or dialect literature.
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