甲 originally meant that “buds open their outer shell in spring”. It serves as a phonetic component to form characters. The position of 甲 in a character: left, right, bottom or inside.
You might also want to check out this component: 甬
Characters formed by the component 甲
钾 岬 胛 玾 jiǎ
匣 狎 柙 舺 炠 翈 筪 xiá
押 庘 鸭 yā
闸 厣 笚 呷 zhá yǎn dā xiā