enthusiasm n.

word-forming element meaning "near, at, in, on, within," from Greek en "in," cognate with Latin in (from PIE root *en "in"), and thus with en- (1). Typically assimilated to em- before -p-, -b-, -m-, -l-, and -r-.

*dhēs-, Proto-Indo-European root forming words for religious concepts. Possibly an extension of PIE root *dhe- "to set, put."

It forms all or part of: apotheosis; atheism; atheous; Dorothy; enthusiasm; fair (n.) "a stated market in a town or city;" fanatic; ferial; feast; fedora; -fest; festal; festival; festive; festoon; Festus; fete; fiesta; henotheism; monotheism; pantheism; pantheon; polytheism; profane; profanity; Thea; -theism; theist; theo-; theocracy; theodicy; Theodore; Theodosia; theogony; theology; theophany; Theophilus; theosophy; theurgy; tiffany; Timothy.

It is the hypothetical source of/evidence for its existence is provided by: Greek theos "god;" Latin feriae "holidays," festus "festive," fanum "temple."