capstone \ˈ ̷ ̷ˌ ̷ ̷\noun (-s) Etymology:cap (I) + stone 1. a.: a coping stone : coping b.: the horizontal topmost stone of a dolmen 2.: the crowning point : most important element : decisive factor : climax, acme < a system of primary and secondary schools … with the university the capstone — American Guide Series: Virginia >