The word expletive comes from the Latin verb explere, meaning "to fill", via expletivus, "filling out". It was introduced into English in the seventeenth century to refer to various kinds of padding — the padding out of a book with peripheral material, the addition of syllables to a line of poetry for metrical purposes, and so forth. Use of expletive for such a meaning is now rare. Rather, expletive is a term in linguistics for a meaningless word filling a syntactic vacancy (syntactic expletives). Outside linguistics, the word is much more commonly used to refer to "bad language". Some linguists use it to refer to meaningless, "filler" use of "bad language" ("expletive attributives"), distinguishing this from meaningful use.