arrowhead
鏑 centers on the metal tip of an arrow: the arrowhead itself. The kun readings extend this to whistling arrowheads (かぶら, かぶらや) and arrowheads in general (やじり).
鏑 combines 金 (metal) with 啇, which likely contributes the sound テキ and relates to the arrowhead's metal construction. The exact historical development of 啇 in this context is uncertain.
The left side is metal 金, and the right side 啇 looks like a pointed object with a base. Picture a metal arrowhead being forged and fitted onto a shaft.
For テキ, imagine a metal arrowhead striking a target with a sharp 'tek' sound: tek -> テキ, the sound of the arrowhead hitting its mark.
horseback archery
eight-holed arrow whistle
turnip-shaped whistle made of hollowed-out wood or deer horn (attached to an arrow to sound when fired)
arrow with a whistle attached; whistling arrow used to signal the start of battle
arrow with a whistle attached; whistling arrow used to signal the start of battle