Just learned this one. Strictly, more than one word, but still, a single dictionary entry. From Wiktionary.
Three sheets to the wind
(idiomatic) Drunk.
That late in the evening, he was three sheets to the wind and had long since stopped making sense.
Derived from sailing ships. The 'sheet' in the phrase uses the nautical meaning, of a rope controlling the trim of sail. A sail (usually a jib sail) is said to be sheeted to the wind, when it is set to backfill (set to the opposite side of the ship from normal use)
A jib sail is not normally kept in backfill position. But in a major storm when a ship must be kept “hove-to” (kept as much as possible in a standstill position and not being blown forward) the helm or wheel is lashed to windward, and the jib(s) are sheeted to the windward side of the ship (sheeted to the wind).
As a storm gets stronger, more backfill counterbalancing is required to hold the ship in position and additional jibs are sheeted to the wind to maintain the ship at a standstill. When a ship has three jibs sheeted to the wind, it is being held sideways to wind and waves in strong storm conditions with very high waves, causing it to roll wildly from side to side with each wave, in continuous danger of rolling over or capsizing.
Hence 'three sheets to the wind' has been used to describe a highly inebriated person who is no longer in control, and is in danger of upending and falling over.