1. Lit. to walk or steer one's vehicle onto a road, highway, or path. Turn onto the main road and go west about a mile. As she turned onto the familiar highway, she realized that she had left her purse in the store.

2. turn onto someone or something Inf. Fig. to become interested in someone or something. Jeff turned onto electronics at the age of fourteen. I tried to get her to turn onto me, but she could only think of John.