From The Collaborative International Dictionary of English v.0.48:
Warder \Ward"er\, n.
1. One who wards or keeps; a keeper; a guard. "The warders of
the gate." --Dryden.
[1913 Webster]
2. A truncheon or staff carried by a king or a commander in
chief, and used in signaling his will.
[1913 Webster]
When, lo! the king suddenly changed his mind,
Casts down his warder to arrest them there.
--Daniel.
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Wafting his warder thrice about his head,
He cast it up with his auspicious hand,
Which was the signal, through the English spread,
This they should charge. --Drayton.
[1913 Webster]