good friend; beneficial friend
A somewhat formal or literary term for a friend who is a positive influence, offering moral or practical benefit. Not used in casual conversation.
A good book is a beneficial friend.
彼は私にとって真の益友だ。
He is a true beneficial friend to me.
three kinds of beneficial friends
Compound of 益 (benefit, advantage) and 友 (friend). The exact historical derivation is uncertain, but the word follows a classical Chinese pattern for describing types of friends.