Si·mul·ta·ne·ous a. Existing, happening, or done, at the same time; as, simultaneous events. -- Si*mul*ta*ne*ous*ly, adv. -- Si*mul*ta*ne*ous*ness, n.
Simultaneous equations Alg., 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.
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simultaneousness
n : happening or existing or done at the same time [syn: simultaneity]