hyphen (n.)

"short dash used to connect two words or separate one," 1620s, from Late Latin hyphen, from Greek hyphen "mark joining two syllables or words," probably indicating how they were to be said or sung. This was a noun use of an adverb meaning "together, in one," literally "under one," from hypo "under" (from PIE root *upo "under") + hen, neuter of heis "one," from PIE root *sem- (1) "one; as one, together with."