The degree of intimacy or familiarity between people; closeness or affection.
二人の親しさは写真からも伝わってくる。
The closeness between the two is apparent even from the photo.
長年の付き合いで親しさが深まった。
Their closeness deepened after years of being together.
親しさのあまり礼を失することもあるので注意が必要だ。
Sometimes familiarity leads to lapses in courtesy, so you need to be careful.