Lewis & Short

ăpex, ĭcis, m. [etym. acc. to Serv. ad Verg. A. 10, 270, and Paul. ex Fest. p. 18 Müll., from apo, to join to, whence aptus; cf. Van. Etym. p. 33], the extreme end of a thing, the point, summit, top (syn.: cacumen, summa, fastigium, culmen, vertex); hence,

  1. I. Lit., the small rod at the top of the flamen’s cap, wound round with wool, Serv. ad Verg. A. 2, 683; 10, 270.
    Hence,
  2. II. Transf.
    1. A. (As pars pro toto.) The conical cap of the flamen, ornamented with this rod: QVEI. APICEM. INSIGNE. DIALIS. FLAMINIS. GESISTEI, Epitaph. Scip. Grotef. 2, 299: apicem dialem, Liv. 6, 41: apex e capite prolapsus, Val. Max. 1, 1, n. 4.
      Hence, of the priesthood itself: homo honestus non apice insignis, Sen. ap. Lact. 17, 6.
    2. B. Any hat or helmet, a crown: ab aquilā Tarquinio apicem impositum putent, Cic. Leg. 1, 1: regum apices, Hor. C. 3, 21, 20: ardet apex capiti, Verg. A. 10, 270; 2, 683.
      Of birds, the crest, Plin. 11, 37, 44, § 121.
    3. C. A projecting point or summit.
      1. 1. Lit., of trees: lauri, Verg. A. 7, 66.
        Of a headland: sublimis, Juv. 12, 72: montis apex, Sil. 12, 709; so Vulg. Judith, 7, 3.
        Of the point of a sickle, Col. 4, 25, 1.
        Of the summit of a flame, Ov. M. 10, 279 et saep.
      2. 2. Trop., the highest ornament or honor, the crown of a thing: apex est senectutis auctoritas, Cic. Sen. 17, 60: hinc apicem Fortuna sustulit, hic posuisse gaudet, Hor. C. 1, 34, 14.
  3. D.
    1. 1. In gram., the long mark over a vowel, Quint. 1, 7, 2; 1, 4, 10; 1, 5, 23; Victor. p. 2469 P.
      Hence, trop.: nullum apicem quaestionis praetermittere, Arn. 3 init.
      1. 2. The forms or outlines of the letters: litterarum apices, Gell. 13, 30, 10; 17, 9, 12.
        Hence (per synecdochen),
    2. E. A letter or any other writing: apicum oblator, Sid. Ep. 6, 8: Augusti apices, i. e. rescripts, Cod. Just. 2, 8, 6 fin.
  4. F. Of the point or apex of a Hebrew letter, put fig. for the least particle, tittle (eccl. Lat.; Gr. ἡ κεραία): iota unum aut unus apex non praeteribit a lege, Vulg. Matt. 5, 18; ib. Luc. 16, 17.