inner lid
Refers to a lid that sits inside a container, often under an outer lid, such as in traditional Japanese tea caddies or stacked boxes.
When I opened the inner lid of the tea caddy, the aroma of matcha spread.
medium-sized lid
Used for a lid of medium size, often in contexts where lids come in different sizes, such as cookware or storage containers. Less common than the 'inner lid' sense.
This pot comes with three types of lids: large, medium, and small.
Compound of 中 (なか, 'inside' or 'middle') and 蓋 (ふた, 'lid'). The reading なかぶた follows standard rendaku voicing.