Lewis & Short

ecce, adv. demonstr. [perh. from locat. form of pronom. stem i, with demonstr. ending -ce; hence, in comedy often scanned ĕce, Corss. Aussp. 2, 636, 1026 sq.
Ribbeck explains ecce as indef. form ec, as in ecquis, ecquando, etc., strengthened by demonstr. ce, Lat. Part. p. 42 sq.; and Curt. refers it to root oc- of oculus; cf. eccere, Gr. Etym. p. 457], points out an object with emphasis, lo! see! behold! (constr. class. with nom. or clause, and ante-class. also with acc.).

  1. I. In gen.: quem quaero, optime ecce obviam mihi est, behold! there comes he I was wishing for, Plaut. Bacch. 4, 4, 16: ecce autem video rure redeuntem senem, Ter. Eun. 5, 4, 45: ecce Dionaei processit Caesaris astrum, Verg. E. 9, 47: ecce trahebatur passis Priameïa virgo Crinibus, id. A. 2, 403; cf. id. ib. 6, 337; Ov. M. 2, 441 al.; sometimes in the middle of a clause: audiat haec tantum—vel qui venit ecce Palaemon, Verg. E. 3, 50; Ov. M. 2, 93: apparet adhuc vetus cicatrix, id. ib. 12, 444; Calp. Ec. 1, 4 al.
  2. II. In partic.
    1. A. To denote that something is present (cf. Fr. voici), here (in this sense mostly ellipt.): circus noster ecce adest, Plaut Fragm. ap. Varr. L. L. 5, § 153 Müll.; so with adest, Ov. M. 2, 496; 3, 101: quid me quaeris? … ecce me, here I am, Plaut. Epid. 5, 2, 15; so, ecce me, id. Curc. 1, 3, 6; id. Mil. 3, 1, 69; Ter. Ad. 5, 9, 38: ecce nos, Plaut. Mil. 3, 1, 17: ecce odium meum, id. Poen. 1, 2, 139: ecce Gripi scelera, id. Rud. 4, 4, 134: ecce tuae litterae de Varrone, Cic. Att. 13, 16: ecce hominem te, Stasime, nihili, Plaut. Trin. 4, 3, 6; and simply ecce, here I am, id. As. 1, 1, 96.
    2. B. In enumerations, or after other objects mentioned, to introduce a new one with emphasis (Ciceronian): consecuti sunt hos Critias, Theramenes, Lysias, etc. … ecce tibi exortus est Isocrates, Cic de Or. 2, 22 fin.; id. Or. 16 fin.; id. de Or. 3, 3, 31; so ellipt., id. Div. 2, 70, 144; id. Ac. 2, 43, 134; id. Pis. 21.
    3. C. To introduce something unexpected or strange; hence, sometimes connected with subito, repente, de improviso, etc.: ecce Apollo mihi ex oraculo imperat, Ut, etc., Plaut. Men. 5, 2, 87; Cic. Sest. 41, 89; id. de Or. 2, 22, 94: et ecce de improviso ad nos accedit cana veritas, Varr. ap. Non. 243, 1; cf. Sall. J. 14, 11: discubitum noctu ut imus, ecce ad me advenit mulier, Plaut. Merc. 1, 1, 99; so with a preceding cum, Cic. Caecin. 7, 20; with dum: haec dum agit, ecce, etc., Hor. S. 1, 9, 60; with ubi, Verg. A. 3, 219.
      Ellipt.: ecce postridie Cassio litterae Capua a Lucretio, Cic. Att. 7, 24; id. Q. Fr. 1, 2, 2, § 6; id. Ac. 2, 38; with subito, id. Att. 8, 8; 10, 3; cf.: ecce autem repente, id. Verr. 2, 5, 34; and with a preceding cum, id. Att. 2, 8; Liv. 2, 36 fin.
      For the expression ecce autem, v. autem.
    4. D. In conversat. lang., combined with the pronouns is, ille, and iste, into one word standing for either the simple ecce, or the pronoun itself, but with demonstrative force, in the foll. forms: nom., ecca, Plaut. Men. 1, 2, 66; id. Rud. 4, 4, 130; Ter. Eun. 1, 1, 34: eccilla, Plaut. Stich. 4, 1, 30: eccillud, id. Rud. 2, 7, 18: acc. sing., eccum, Plaut. Am. prol. 120; 1, 2, 35; 3, 4, 22 et saep.; Ter. And. 3, 2, 52; 3, 3, 48 et saep.; Titin. ap. Charis. p. 177 P.: eccam, Plaut. Am. 2, 2, 146; id. As. 1, 2, 25; id. Cas. 2, 1, 15 et saep.; Ter. Eun. 4, 5, 12; id. Hec. 4, 1, 8: eccillum, Plaut. Merc. 2, 3, 98; id. Pers. 2, 2, 65; id. Trin. 3, 1, 21; and syncopated ellum, Ter. And. 5, 2, 14; id. Ad. 2, 3, 7; Plaut. Curc. 2, 2, 28: eccillam, and sync. ellam, Ter. Ad. 3, 3, 35; Plaut. Aul. 4, 10, 51; id. Mil. 3, 1, 194; eccistam, Plaut. Curc. 5, 2, 17: plur., eccos, id. Bacch. 3, 2, 19; id. Most. 1, 3, 154; id. Mil. 4, 7, 27; 5, 35; id. Rud. 2, 2, 4; Ter. Heaut. 2, 3, 15; Afran. ap. Charis. p. 95 P.: eccas, id. Rud. 3, 2, 49: ecca, Plaut. Rud. 4, 4, 110.
      On the construction of eccum, etc., cf. Brix ad Plaut. Capt. 1002, p. 72; and on ecce see Hand, Turs. II. pp. 343-351.