Definition of "weightiest"

THE CONCISE ENCYCLOPAEDIA OF WORLD RAILWAY LOCOMOTIVES. Edited by P. Ransome-Wallis. Hutchinson. 50s.A gaudy jacket, remarkably out of keeping with the contents, camouflages the weightiest and meatiest work on a railway topic since the war.

1960 January, “New reading on railways”, in Trains Illustrated, page 26