noun

• (mathematics) Oneness, singularity, seen as a component of a whole number; a magnitude of one.
  "Number, we define, to be, a certayne Mathematicall Sũme, of Vnits. [Note the worde, Vnit, to expresse the Greke Monas, & not Vnitie: as we haue all, commonly, till now, vsed.]"
• (sciences) A standard measure of a quantity or magnitude.
  "The centimetre is a unit of length."
• (military, informal) A member of a military organization.
  "The fifth tank brigade moved in with 20 units. (i.e., 20 tanks)"
• (commerce) An item which may be sold singly.
  "We shipped nearly twice as many units this month as last month."

adj

• (mathematics) Having a size or magnitude of one.
  "Consider the following time sequence Z_t=A sin (ωt+θ), where A is a random variable with a zero mean and a unit variance and θ is a random variable with a uniform distribution on the interval [-π,π] independent of A."