A.T. Robertson Commentary Luke 8:37

"And all the people of the country of the Gerasenes round about asked him to depart from them, for they were holden with great fear: and he entered into a boat, and returned." — Luke 8:37 (ASV)

Were holden with great fear (φοβω μεγαλω συνειχοντο). Imperfect passive of συνεχω with the instrumental case of φοβος. See a similar use of this vigorous verb in Lu 12:50 of Jesus and in Php 1:23 of Paul.