The cardinal number following eighty and preceding eighty-two.

None at all.

Having only one arm; especially having lost an arm.

Having only one leg. / Of an audio signal: having a thin sound as a result of connection through only one wire of a circuit pair.

A plant, especially a tree.

(computing) The number obtained by subtracting a given n-digit binary number from 2ⁿ-1 (which yields the same result as the logical complement).

(biblical) The Devil; Satan; Lucifer.

Allowing movement in only one direction; unidirectional. / Allowing travel in only one direction.

(agriculture) To use a disc harrow to turn the soil and kill weeds, in preparation for planting seeds.

(idiomatic) Close to death.