International Standard Bible Encyclopedia (1915)
A division of the night. The night was originally divided into three watches (Jud 7:19), but later into four, as we find in the (Mt 14:25; Mr 6:48). We do not know the limits of the watches in the first division, but the middle watch probably began two hours before midnight and ended two hours after. The fourfold division was according to the Roman system, each of which was a fourth part of the night.
"Watch" is also the guard placed on watch (mishmar, Ne 4:9; koustodia, from Latin custodia, Mt 27:65,66; 28:11). It sometimes refers to the act of watching, as in 2Ki 11:6,7 (mishmereth); Lu 2:8 (phulake).
"Watch" is also used figuratively, as in Ps 141:3 for restraint: "Set a watch, O Yahweh, before my mouth" (shomrah).