Definition of Rereward:

1. rear guard
2. the back or rear
   

Examples:

Joshua 6:9 And the armed men went before the priests that blew with the trumpets, and the rereward came after the ark, the priests going on, and blowing with the trumpets.

Joshua 6:13 And seven priests bearing seven trumpets of rams' horns before the ark of the LORD went on continually, and blew with the trumpets: and the armed men went before them; but the rereward came after the ark of the LORD, the priests going on, and blowing with the trumpets.

1 Samuel 29:2 And the lords of the Philistines passed on by hundreds, and by thousands: but David and his men passed on in the rereward with Achish.

Isaiah 52:12 For ye shall not go out with haste, nor go by flight: for the LORD will go before you; and the God of Israel will be your rereward.

Isaiah 58:8 Then shall thy light break forth as the morning, and thine health shall spring forth speedily: and thy righteousness shall go before thee; the glory of the LORD shall be thy rereward.