1) Imprecise 2) Indefinable 3) Indefinite 4) Mathematical terminology 5) Uncertain 6) Undefinable 7) Undefined feelings of sadness 8) Undetermined 9) Unfixed 10) Vague 11) Without fixed limits 1) Indefinable 2) Indefinite 3) Undefinable 4) Vague 
[mathematics] In mathematics, the word undefined has several different meanings, depending on the context. See extended real number line for more information. ...
an aspect of C++'s semantics for which no reasonable behavior is required. An example is dereferencing a pointer with the value zero. Avoid undefined behavior. See also: implementation defined. TC++PL C.2.
[adj] - not precisely limited, determined, or distinguished
adjective not precisely limited, determined, or distinguished; `an undefined term`; `undefined authority`; `some undefined sense of excitement`; `vague feelings of sadness`; `a vague uneasiness`
without fixed limits; indefinite in form, extent, or application: undefined authority; undefined feelings of sadness. · not given meaning or significance, as by a definition; not defined or explained: an undefined term.