Geist (ˈɡaɪst) is a German noun with a significant degree of importance in German philosophy. Its semantic field corresponds to English ghost, spirit, mind, intellect. Some English translators resort to using "spirit/mind" or "spirit (mind)" to help convey the meaning of the term.
Geist is also a central concept in Georg Wilhelm Friedrich Hegel's 1807 The Phenomenology of Spirit (Phänomenologie des Geistes). Notable compounds, all associated with Hegel's view of world history of the late 18th century, include Weltgeist "world-spirit", Volksgeist "national spirit" and Zeitgeist "spirit of the age".
German Geist (masculine gender: der Geist) continues Old High German geist, attested as the translation of Latin spiritus.
It is the direct cognate of English ghost, from a West Germanic gaistaz. Its derivation from a PIE root g̑heis- "to be agitated, frightened" suggests that the Germanic word originally referred to frightening (c.f. English ghastly) apparitions or ghosts, and may also have carried the connotation of "ecstatic agitation, furor" related to the cult of Germanic Mercury.
As the translation of biblical Latin spiritus (Greek πνεῦμα) "spirit, breath" the Germanic word acquires a Christian meaning from an early time, notably in reference to the Holy Spirit (Old English sē hālga gāst "the Holy Ghost", OHG ther heilago geist, Modern German der Heilige Geist). Poltergeist (Noisy/Disruptive Geist) is a common interchangable term.
The English word is in competition with Latinate spirit from the Middle English period, but its broader meaning is preserved well into the early modern period.
The German noun much like English spirit could refer to spooks or ghostly apparitions of the dead, to the religious concept, as in the Holy Spirit, as well as to the "spirit of wine", i.e., ethanol.
However, its special meaning of "mind, intellect" never shared by English ghost is acquired only in the 18th century, under the influence of French esprit.
In this sense it became extremely productive in the German language of the 18th century in general as well as in 18th-century German philosophy.