Shirabe

死語しご

Common Noun
English jmdict
1
noun (common) (futsuumeishi) dead language;extinct language
しかし、その一方、ラテン語はそのときまでに「死語」となっていた。
But, then again, Latin was already a "dead language" by that time.
2
noun (common) (futsuumeishi) obsolete word;dated word;word that has become passé
See also: 廃語 (はいご)
それって死語じゃないの。
People don't say that anymore.