c.1200, "to entrap," in the same sense as O.E. underniman (cf. Du. ondernemen, Ger. unternehmen), of which it is a partial loan-translation, from under + take. Cf. also Fr. entreprendre "to undertake," from entre "between, among" + prendre "to take."
The under in this word may be the same one that also may form the first element of understand. Meaning "to accept" is attested from mid-13c.; that of "to take upon oneself, to accept the duty of" is from c.1300. Undertaking "enterprise" is recorded from early 15c.