Plain English Meaning
Anti-icing means stopping ice from forming in the first place. You turn the system on before ice can build up, so the protected parts stay clear.
Full Definition
A system or procedure that prevents ice from forming on aircraft surfaces or components by activating before ice accumulation begins. Anti-icing is preventive — it is turned on in advance of, or upon entering, icing conditions to keep protected surfaces clean.
Context Anchor
Seen in aircraft systems discussions, winter operations, preflight planning, and checklist items for operating in visible moisture near freezing temperatures.
Derivation
From the prefix 'anti-' (Latin/Greek, meaning 'against' or 'preventing') combined with '.' The word literally means 'against ice forming' — which captures the idea: it acts before ice appears, not after.