Albert Barnes Commentary Judges 9:31

"And he sent messengers unto Abimelech craftily, saying, Behold, Gaal the son of Ebed and his brethren are come to Shechem; and, behold, they constrain the city [to take part] against thee." — Judges 9:31 (ASV)

Secretly - See the margin. The word is probably the name of a place in “Tormah”; some think the same as “Arumah” (Judges 9:41). Zebul was faithful to Abimelech but dissembled his sentiments, from being too weak to oppose Gaal, until Abimelech came with his army (Judges 9:38).