A hoard is a hidden store — a hoard of coins, a hoard of tinned food. A horde is a large crowd, usually of people and often unruly. Hoard is also a verb: to accumulate and hide away. Horde is only ever a noun.
The core difference
Homophones with unrelated meanings, and one of them is also a verb.
- hoard — a hidden store: a Viking hoard. As a verb: to stockpile.
- horde — a large crowd: hordes of tourists.
The origins
Hoard is Old English, related to treasure. Horde came into English from Turkic through Polish — the Golden Horde being the Mongol khanate — and originally meant a nomadic camp or tribe. The crowd sense grew from that.
Which one archaeologists use
Hoard, always — the Staffordshire Hoard, the Sutton Hoo finds. Anything buried and rediscovered is a hoard, never a horde.