Derived from spīrō ("I breathe, I respire; I live").
From a breath of air to the breath of life, from a light breeze to an energy; spiritus, in all of its meanings, refers to an immaterial essence or substance. The English derivative of spiritus, spirit, also has a complex history and many varying meanings which makes it difficult to pin down in words.
Below are the first 3 definitions of spirit as documented by The Oxford English Dictionary:
I. An animating or vital principle; the immaterial or sentient element of a person.
* An animating or vital principle; the soul; incorporeal or immaterial being.
a. The animating or vital principle in humans and animals; that which gives life to the body, in contrast to its purely material being; the life force, the breath of life.
b. In expressions indicating or implying that this principle has been diminished or has ceased, causing unconsciousness or death, or that it has recovered, causing consciousness or life to return.
c. In extended and figurative use. Frequently collocated with life; cf.
a. The immaterial aspect of a person, considered as a separable part of a person (which persists after death); esp. (in Christian context) this considered as a moral agent and in relation to God; a person's soul. Frequently in phrases referring to a person's death. Cf.
3. As a mass noun. Incorporeal, immaterial, or abstract being, as opposed to body or matter; being or intelligence conceived as distinct from, or independent of, anything physical or material. Cf. MIND: As a mass noun: the mental entity or faculties, esp. as opposed to matter