From phulasso; a guarding or (concretely, guard), the act, the person; figuratively, the place, the condition, or (specially), the time (as a division of day or night), literally or figuratively -- cage, hold, (im-)prison(-ment), ward, watch.

see GREEK phulasso

a. in an active sense, a watching, keeping watch: φυλάσσειν φυλακάς, to keep watch, Luke 2:8 (often in the Greek writings from Xenophon, an. 2, 6, 10, etc.; Plato legg. 6, p. 758 d. down; (cf. φυλακάς ἔχειν, etc. from Homer (Iliad 9, 1 etc.) on); often also in the Sept. for מִשְׁמָרות שָׁמַר).

b. like the Latincustodia and more frequently the pluralcustodiae (see Klotz, Hdwrbch. (or Harpers' Latin Dict.) under the word), equivalent to persons keeping watch, a guard, sentinels: Acts 12:10 (here A. V. ward) (and very often in secular authors from Homer down).

c. of the place where captives are kept, a prison: Matthew 14:10; Matthew 25:36,(39),43f; Mark 6:17, 27(28); Luke 3:20; Luke 21:12; Luke 22:33; Acts 5:19, 22; Acts 8:3; Acts 12:5f, 17; Acts 16:27, 40; Acts 22:4; Acts 26:10; 2 Corinthians 6:5 (here, as in Hebrews 11:36, A. V. imprisonment); 2 Corinthians 11:23; 1 Peter 3:19; Revelation 18:2 (twice; rendered in A. V. hold and cage (R. V. hold)); (Herodotus 3, 152; Thucydides 3, 34; Plutarch, others; the Sept. for מַטָּרָה, כֶּלֶא בֵּית, and הַכֶּלֶא בֵּית, מִשְׁמָר); βάλλειν or τιθέναι τινα εἰς (τήν) φυλακήν or ἐν (τῇ) φυλακή: Matthew 5:25; Matthew 14:3 (R G, others, ἀπέθετο); ; Luke 12:58; Luke 23:19, 25; John 3:24; Acts 5:25; Acts 8:3 (here παραδιδόναι εἰς φυλακήν); ; Revelation 2:10.

d. of the time (of night) during which guard was kept, a watch i. e. the period of time during which a part of the guard were on duty, and at the end of which others relieved them. As the earlier Greeks divided the night commonly into three parts (see Liddell and Scott, under the word I. 4), so, previously to the exile, the Israelites also had three watches in a night; subsequently, however, after they became subject to Rome, they adopted the Roman custom of dividing the night into four watches: Matthew 24:43; ἐν τῇ δευτέρᾳ, τρίτῃ, Luke 12:38; τετάρτῃ, Matthew 14:25; Mark 6:48. Cf. Winer's RWB under the word Nachtwache; (McClintock and Strong's Cyclopaedia, under the word ; B. D. under the phrase, ).