Definition of "gigantesque"

As Smythe took the handles and they turned the great corner of the street, Angus was amused to see a gigantesque poster of “Smythe’s Silent Service,” with a picture of a huge headless iron doll, carrying a saucepan with the legend, “A Cook Who is Never Cross.”

1911, G. K. Chesterton, “The Invisible Man”, in The Innocence of Father Brown