オタク

• おたく (otaku), ヲタク (otaku)
• (short) オタ (ota), ヲタ (ota)

From お宅 (otaku), the honorific version of 宅 (taku, “home”), referring to 1982–1983 Macross fans, or perhaps earlier; see Wikipedia discussion.

• (Tokyo) オタク [òtákú] (Heiban – [0])
• IPA^(key): [o̞ta̠kɯ̟]

オタク • (otaku) 

1. (chiefly derogatory) geek, nerd, freak, no-lifer; one who is obsessed with something to the exclusion of such things as social interaction.
   • 2002, 山田裕康 [Yamada Hiroyasu], LDの可能性を広げる, page 11:

     しかし、多(おお)くの友(とも)達(だち)にとってはそんなことにはまったく興(きょう)味(み)はなく、「またかよ〜」と飽(あ)き飽(あ)きしているのですが、「電(でん)車(しゃ)の時(じ)刻(こく)表(ひょう)」、「ポットン便(べん)所(じょ)」、「明(あけ)智(ち)光(みつ)秀(ひで)」、「テレビ番(ばん)組(ぐみ)の細(こま)かすぎるオタク」と、どんな話(わ)題(だい)からもルド君(くん)はそちらに持(も)って行(い)ってしまうのです。

     Shikashi, ōku no tomodachi ni totte wa sonna koto ni wa mattaku kyōmi wa naku,“mata ka yo~” to akiaki shiteiru no desu ga,“densha no jikokuhyō”,“potton benjo”,“Akechi Mitsuhide”,“terebi bangumi no komakasugiru otaku” to, donna wadai kara mo Rudo-kun wa sochira ni motte itte shimau no desu.

     (please add an English translation of this example)

   • 2004, Jim Albert, Jay Bennett, translated by 加藤貴昭 [Katō Yoshiaki], メジャーリーグの数理科学 (上) [Major league mathematical science (first part)], page 58:

     統(とう)計(けい)学(がく)者(しゃ)は所(しょ)詮(せん)、数(すう)字(じ)オタクやグラフ作(さく)成(せい)者(しゃ)と思(おも)われがちだが、それは明(あき)らかに間(まち)違(が)った解(かい)釈(しゃく)である。

     Tōkeigakusha wa shosen, sūji otaku ya gurafu sakuseisha to omoware gachi da ga, sore wa akiraka ni machigatta kaishaku dearu.

     Statisticians are after all liable to be thought of as number geeks and graph makers, but that is obviously a mistaken interpretation.

   • 2006, 亜洲奈みづほ [Asuna Mizuho], 台湾事始め:

     今(いま)や日(に)本(ほん)でも茶(ちゃ)芸(げい)館(かん)が、エキセントリックなオタクではなく、おしゃれな女(じょ)性(せい)たちに楽(たの)しまれるようになった。

     Ima ya Nihon de mo chageikan ga, ekisentorikku na otaku de wa naku, oshare na josei-tachi ni tanoshimareru yō ni natta.

     And now in Japan as well tea houses have come to be enjoyed not by eccentric geeks but by stylish women.

• Unlike in English, where the word otaku is used to refer to fans of anime and manga specifically, this term can be used to denote people with a heavy interest in any other topic, theme or hobby.
• The term has recently gained derogatory connotations in its mainstream usage, whereas its non-derogatory usage continues mostly in its shortened forms オタ (ota) and ヲタ (ota) (see アニオタ (aniota, “anime fan”), 鉄オタ (tetsuota, "railway fan")).

• “同人用語の基礎知識/ Otaku”: a fairly comprehensive description in Japanese of the word and its origins.