Webster's Revised Unabridged Dictionary · 1913

Simultaneous

Simultaneous , adjective

[Late Latin simultim at the same time, from Latin simul. See Simulate.]

Existing, happening, or done, at the same time; as, simultaneous events.
Collocations (1)
Simultaneous equations (Algebra) , two or more equations in which the values of the unknown quantities entering them are the same at the same time in both or in all.