Lexical Definition

‎φυλακτήριον‎ phylaktḗrion (foo-lak-tay'-ree-on) phylactery ^G:N-N
neuter of a derivative of ‎φυλάσσω‎

phylactery.

• a guard-case, i.e. "phylactery" for wearing slips of Scripture texts

Abbott-Smith

* φυλακτήριον, -ου, τό
1. an outpost, fortification (Thuc., al.).
2. a safeguard (Plat.).
3. an amulet (Plut., al.); in NT for the Talmudic תְּפִלִּין, a prayer fillet, a phylactery, a small strip of parchment on which portions of the law were written and worn on the forehead and next the heart (cf. Ex 13:16): Mt 23:5.†

Abbott-Smith References

Liddell-Scott-Jones

φυλακτήριον-τήριον, τό,

guarded post, fort, castle, [Refs 5th c.BC+]: especially an outpost communicating with fortifications, [Refs 5th c.BC+]: plural, guardrooms, [Refs 4th c.BC+]

__2 safeguard, security, [Refs 5th c.BC+]: preservative, [Refs 4th c.BC+]; amulet, [Refs 1st c.AD+]; among the Jews φυλακτήρια were small rolls of parchment with texts from the Law written on them, bound to the forehead by persons praying, [NT]; φ. χρυσᾶ, symbols denoting the kingdoms of Upper and Lower Egypt, [Refs 2nd c.BC+]; amulet, [Refs]
__3 perhaps guard or chain, PLond.unpublished2199.

_{LSJ Scripture Refs: Matt.23.5}