inseam; inside leg
Refers to the length from the crotch to the hem of trousers or pants. Commonly used in clothing sizes and tailoring.
The inseam of these trousers is too long.
股下を測ってからパンツを注文した。
I ordered the pants after measuring my inside leg.
Compound of 股 (mata, 'crotch') and 下 (shita, 'below'). The reading またした is a straightforward combination of the kun'yomi readings of the two kanji.