Encyclopaedia Britannica 15th edition

Soul: an immaterial principle or aspect that, with the body, constitutes the human person। The soul has also been conceived as the very essence of a thing and not a mere aspect or part.

Although now closely associated with such terms as mind, spirit, or self, with which it has become almost synonymous, the basic connotation of soul in ancient and primitive societies was life. Soul is the life of the body. ... At death the soul leaves the body, and all bodily processes cease.