Adam Clarke on Luke 24:19

Which was a prophet - Ανηρ προφητης, a man prophet, a genuine prophet; but this has been considered as a Hebraism: "for, in Exo 2:14, a man prince is simply a prince; and in 1Sam 31:3, men archers mean no more than archers." But my own opinion is, that this word is often used to deepen the signification, so in the above quotations: Who made thee a man prince (i.e. a mighty sovereign) and a judge over us! Exo 2:14. And, the battle went sore against Saul, and the men archers (i.e. the stout, or well aiming archers) hit him, 1Sam 31:3. So in Palaephatus, de Incredib. c. 38. p. 47, quoted by Kypke, ην ανηρ βασιλευς μεγας, He was a great and eminent king. So ανηρ προφητης here signifies, he was a Genuine prophet, nothing like those false ones by whom the people have been so often deceived; and he has proved the divinity of his mission by his heavenly teaching, and astonishing miracles.

Mighty in - word - Irresistibly eloquent. Powerful in deed, working incontrovertible miracles. See Kypke in loco.