A substance or device that causes something to become fluid, or any agent that promotes flowing or liquefaction.
From 'fluidify' (to make fluid) plus the agent suffix '-er' (one who does), creating a noun for substances or devices that facilitate fluidification.
Chemists use fluidifiers like thinner in paint or plasticizers in plastic—they're hidden heroes that make materials flow where they'd normally stick, and they're everywhere in manufacturing.
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