The word spirit can have a very wide meaning. It is derived from the Latin word spiritus, meaning a breath. Then because the soul of man is as invisible to bodily eyes as a breath, and also because its presence is manifested by the breathing of a living body, the word spirit acquired a transferred sense, becoming a substitute for the word soul. If then we intend by the word spirit the principle of life in a man, that principle which enables him to live, to know and to love, to be happy or to be sorrowful, then the spirit is the soul. And in a further sense, because a man’s dispositions depend upon his soul, we use the word spirit for character, and thus speak of a man’s spirit. But this is only the soul, manifesting itself in a man’s external conduct. The soul, therefore, is the living principle which makes the difference between a living man and a corpse, and spirit and soul in this sense mean the same thing.
Existence and nature of the soul, Question 30 from Radio Replies Volume I Copyright © 1938 (by Rev. Dr. Leslie Rumble, M.S.C. and Rev. Charles Mortimer Carty).