δεῖ
Etym. from δέω1, "to bind"
I. c. acc. pers. et inf., δεῖ τινὰ ποιῆσαι "it is binding on" one to do a thing, "one must, one ought", Lat. oportet, Hom., etc.:—rarely, δεῖ σε ὅπως δείξεις ῀ δεῖ σε δεῖξαι, Soph.: —rarely also c. dat. pers. et inf., "there is need" for one to do, δεῖ τινὶ ποιήσαι Eur., Xen.
2. c. acc. rei et inf., δεῖ τι γενέσθαι Thuc., etc.:—for the phrase οἴομαι δεῖν, v. οἴομαι:— when used absol., an inf. may be supplied, μὴ πεῖθ᾽ ἃ μὴ δεῖ (sc. πείθειν) Soph., etc.
II. (from δέω2, "to want)", c. gen. rei, "there is need of, there is wanting", Lat. opus est re, οὐδὲν δεῖ τινός Hdt., attic:—phrases, πολλοῦ δεῖ "there wants much, far from it"; ὀλίγου δεῖ "there wants little, all but":— in answers, πολλοῦ γε δεῖ, πολλοῦ γε καὶ δεῖ far from it, Ar., Dem.; πλεῦνος δεῖ "it is still further from it", Hdt:— ὀλίγου δεῖν absol., in same sense, Plat.; μικροῦ δεῖν Dem.
2. with a dat. pers. added, δεῖ μοί τινος, Lat. opus est mihi re, Aesch., Thuc., etc.
3. with acc. pers. added, δεῖ σε προμηθέως Aesch.
III. neut. part. δέον, contr. δεῖν, absol., like ἐξόν, παρόν "it being needful, quum oporteret", Plat.; οὐκ ἀπήντα, δέον, he did not appear in court, "though he ought to have done so", Dem.; so, οὐδὲν δέον "there being" no "need", Hdt.
II. for δέον, τό, as Subst., v. sub voce.