Vine's Expository Dictionary of NT Words
an adjective signifying "running forward, going in advance," is used as a noun, of "those who were sent before to take observations," acting as scouts, especially in military matters; or of "one sent before a king" to see that the way was prepared, Isaiah 40:3; (cp. Luke 9:52; and, of John the Baptist, Matthew 11:10 , etc). In the NT it is said of Christ in Hebrews 6:20 , as going in advance of His followers who are to be where He is, when He comes to receive them to Himself. In the Sept., Numbers 13:21 , "forerunners (of the grape);" Isaiah 28:4 , "an early (fig)."
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Vines, W. E., M. A. Entry for 'Forerunner'. Vine's Expository Dictionary of NT Words. https://www.studylight.org/dictionaries/eng/ved/f/forerunner.html. 1940.