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1590s, "narrow, drawn in, small," from Latin strictus "drawn together, tight, rigid," past participle of stringere "draw or bind tight" (see strain (v.)). The sense of "stringent and rigorous" (of law) is first found in 1570s; of qualities or conditions generally, 1580s.
A function f is strict in an argument if
f bottom = bottom
(See bottom). In other words, the result depends on the argument so evaluation of an application of the function cannot terminate until evaluation of the argument has terminated.
If the result is only bottom when the argument is bottom then the function is also bottom-unique.
See also strict evaluation, hyperstrict.