confidante

   

confidante:

【名】confidant(男の親友)の女性形、親友 
http://eow.alc.co.jp/

confidant:
a person you trust and share your feelings and secrets with
http://dictionary.cambridge.org/define.asp?key=16082&dict=CALD

Who would have guessed, in our gabby tell-all culture, that people interviewed in the 2004 General Social Survey would report an average of only two “core” confidants with whom they “discuss important matters,” down from the mean of three close ties elicited by the same question in 1985?
(July 16, 2006, New York Times)
ちょっと古い記事から例文を取りましたが、親友と呼べる友達の数が減ってきたことを問題視している内容です。

 - 語彙力増強