From Japanese-German FreeDict Dictionary ver. 0.2.0:
釦 /(en)tʃˈaɪniːz(ja)lˈe̞tə/, 鈕 /(en)tʃˈaɪniːz(ja)lˈe̞tə/, () [gai1] [ichi1] ボタン /bˈo̞täɴ/, ぼたん /bˈo̞täɴ/
(noun (common) (futsuumeishi))
Note: word usually written using kana alone (kanji is only used for push-buttons)
botão(1) (m) Knopf, (2) (f) Taste, (m) Knopf, (m) Button