Thayer's Greek Lexicon

 1. a fortified place provided with a garrison, a station for a
guard or garrison
2. a preservative or safeguard , an amulet. The Jews used this word
to describe small strips of parchment on which were written the
following passages of the law of Moses, Ex. 13:1-10, 11-16; Dt.
6:4-9, 11:13-21, and which, enclosed in small cases, they were
accustomed when engaged in prayer to wear fastened by a leather
strap to the forehead and to the left arm over against the heart,
in order that they might thus be solemnly reminded of the duty of
keeping the commands of God in the head and in the heart,
according to the directions given in Ex. 13:16, Dt. 6:8, 11:18;
These scrolls were thought to have the power, like amulets, to
avert various evils and to drive away demons. The Pharisees were
accustomed to widen, make broad, their phylacteries, that they
might render them more conspicuous and show themselves to be more
eager than the majority to be reminded of the law of God.