Lewis & Short

dĭū (old form dĭūs, Orell. Inscr. 8206), adv. [old acc. form of duration of time; root in dies; v. Corss. Ausspr. 1, 232 sqq.].

      1. 1. (Acc. to dies, I. B. 2.) By day (very rare), Manil. 4, 823; usually with noctu: noctuque et diu, Plaut. Cas. 4, 4, 5: noctu diuque, Titin. and Sall. H. Fragm. ap. Charis. p. 185 P. (Sall. H. 2, 54 Dietsch); Sall. J. 38, 3; 44, 5; 70, 1: nec noctu, nec diu, Plaut. Fragm. ap. Non. 98, 27: diu noctuque iter properabunt, Tac. A. 15, 12 fin.: noctu diuque hostibus obniti, id. H. 2, 5.
      2. 2. (Acc. to dies, II. A. 3.; lit., a space of time, a while; hence, with intens. signif.) A long time, long while, long (freq. in all periods; cf.: pridem, dudum): nimis diu et longum loquor, Plaut. Ps. 2, 3, 21; cf. so with longum, id. Ep. 3, 2, 40: diu multumque scriptitare, Cic. de Or. 1, 33, 152; so, diu multumque, id. Or. 1; id. Phil. 13, 5; id. Sull. 26, 73; Sall. J. 94, 3; Flor. 2, 3, 5; also: multum diuque, Cic. de Sen. 3 fin.: multum et diu, id. Agr. 2, 32, 88; id. Inv. 2, 19, 58: multum ac diu, App. M. 2, p. 126, 6; cf. also: recordatus multum et diu cogitavi … Eam rem volutavi et diu disputavi, Plaut. Most. 1, 2, 1 and 4: saepe et diu, Cic. Quint. 31, 96; cf.: saepe diuque, Hor. Ep. 1, 13, 1; diu diuque, App. M. 5, p. 167, 16; 12, p. 266, 16: diu atque acriter pugnatum est, Caes. B. G. 1, 26; 3, 21 et saep.: diu ego hunc cruciabo, Plaut. Capt. 3, 5, 73: Stoici diu mansuros aiunt animos: semper, negant, Cic. Tusc. 1. 31 fin.: diu princeps oratorum, aliquando aemulus Ciceronis, Quint. 11, 3, 8: tam diu restitisti, Plaut. Most. 3, 2, 100: tam diu, id. Mil. 3, 1, 34; id. ib. 4, 2, 89; Ter. Ad. 2, 2, 27; id. Hec. 4, 4, 23; id. Phorm. 1, 3, 13: eo, quo jam diu Sum judicatus, Plaut. Men. 1, 1, 20; so, jam diu, id. Capt. 4, 2, 102; id. Most. 1, 3, 144; id. Poen. 5, 4, 29; cf.: diu est jam, id. Most. 1, 4, 25: ille vult diu vivere, hic diu vixit: quamquam, O di boni! quid est in hominis vita diu? Cic. de Sen. 19, 68 and 69; cf.: sat diu vixisse, Plaut. Capt. 4, 2, 12: nimis diu maceror, id. Ep. 3, 1, 2; so, nimis diu, id. Merc. 1, 54; id. Pers. 4, 4, 105: non diu apud hunc servies, id. Pers. 4, 4, 65; cf.: haud diu, id. Mil. 2, 1, 17; Ter. Eun. 2, 3, 67.
        Followed by dum, donec: diu expectare, dum, etc., Suet. de Rhet. 1: diu jacere donec, etc., Tac. G. 45.
        Comp.: diūtius, longer [the t inserted, as in sectius and setius from secus, being a remnant of adv. ending -ter or -tus]: nolo te jactari diutius, Plaut. Trin. 3, 2, 59; id. Rud. 1, 2, 5; Ter. Heaut. 1, 1, 50; id. ib. 3, 1, 15; Cic. Lael. 27, 104; id. Rosc. Am. 7 fin.; Caes. B. G. 1, 16, 5; id. ib. 1, 26, 1 et saep.: cf.: minus diu quam, Cic. Att. 7, 3, 1.
        In the historians freq. = a long while, very long, no comparison being intended: ne diutius commeatu prohiberetur, Caes. B. G. 1, 49; 3, 9, 5; 3, 29, 2; 4, 35, 2; 7, 20, 5 et saep.: neque illis, qui victoriam adepti forent, diutius ea uti licuisset, Sall. C. 39, 4: legiones diutius sine consulari fuere, Tac. H. 1, 9.
        Sup.: (Cato) qui senex diutissime fuisset, Cic. Lael. 1, 4; so id. Pis. 37; id. de Imp. Pomp. 5 fin.; Caes. B. G. 6, 21, 4; Suet. Vit. 14 al.: ut quam diutissime te jucunda opinione oblectarem, Cic. Q. Fr. 1, 1, 1; so with quam, Caes. B. C. 3, 102, 3.
    1. B. Long since, a great while ago (mostly ante-class.): quod arci, diu facti, celeriter corruissent, Varr. ap. Non. 77, 14; cf.: scelus, inquam, factum’st jam diu antiquom et vetus, Plaut. Most. 2, 2, 45; so, jam diu, id. Ep. 1, 1, 9; id. Men. 2, 3, 28; id. Ps. 1, 3, 4; Ter. Eun. 5, 6, 1; Cic. Att. 1, 19, 9 al.; for which: diu jam, Plin. 25, 1, 1, § 2; id. 19, 4, 15, § 40: is ex Anactorio … huc commigravit in Calydonem haud diu, not long ago, a short time ago, Ter. Ad. 4, 5, 15: nec loci gnara sum, nec diu hic fui, it is not long since I was here, Plaut. Rud. 1, 3, 28: jam diu est factum, quom discesti ab hero, id. As. 2, 1, 3.
      With foll. quom, id. Merc. 3, 1, 44.
      With postquam, id. Pers. 5, 2, 41.
      With quod, id. Am. 1, 1, 146; August. Retract. 1 Prol.
    2. C. In Mela repeatedly of place, a long way: Italia … inter superum mare et inferum excurrit diu solida, Mel. 2, 4, 1; so id. 1, 2, 3; id. 1, 3, 5. Cf. Hand Turs. II. pp. 285-291.