δεῖ impersonal (δέω),

[in LXX chiefly for infin. with לְ ;]

one must, it is necessary: with inf. Mat.26:54, Mrk.13:7, Act.5:29, al.; with accusative and inf. Mat.16:21, Mrk.8:31, Jhn.3:7, Act.25:10, al.; with ellipse of accusative, Mat.23:23; of accusative, and inf. Mrk.13:14, Rom.1:27 8:26; οὐ (μὴ) δεῖ (non licet), ought not, must not: Act.25:24, 2Ti.2:24; impf. ἔδει, of necessity or obligation in past time regarding a past event (Bl. § 63, 4), Mat.18:33, Luk.15:32, Jhn.4:4, Act.27:21, al.; periphr. δέον ἐστίν (as in Attic, χρεών ἐστι = χρή, see: δέον), Act.19:36; id. with ellipse of ἐστίν, 1Pe.1:6 τὰ μὴ δέοντα (= ἃ οὐ δεῖ 1Ti.5:13.

SYN.: ὀφείλει, expressing moral obligation, as distinct from δεῖ, denoting logical necessity and χρή, a need which results from the fitness of things (see Tr. Syn. § cvii, 10; Westc. on Heb.2:1, 1Jn.2:6; Hort on Jas.3:10). (AS)

one must, it is necessary; ought not, must not