Composed of 友 (tomo, "friend, companion") and 達 (tachi/dachi), a suffix indicating plurality or a group of people. 友 alone already means "friend," and 達 originally meant "to reach" or "to attain" in classical Chinese before being borrowed into Japanese as a pluralizing suffix. The compound 友達 is first attested in early modern Japanese and became the standard everyday word for "friend."

In Japanese social culture, the concept of friendship often carries layers of in-group (内, uchi) and out-group (外, soto) dynamics. A 友達 is someone firmly in your uchi circle. Note that 友達 is technically already plural in feel (due to 達), so Japanese speakers rarely need to add further pluralizing words. False-friend warning for learners of both Japanese and Korean: the Korean word 친구 (chingu) covers a very similar meaning but has different nuances around age and hierarchy — Japanese 友達 can be used more flexibly across slight age differences.