flexor retinaculum

noun

flexor ret·​in·​ac·​u·​lum -ˌret-ᵊn-ˈak-yə-ləm 

1

: a fibrous band of fascia on the medial side of the ankle that extends downward from the medial malleolus of the tibia to the calcaneus and that covers over the bony grooves containing the tendons of the flexor muscles, the posterior tibial artery and vein, and the tibial nerve as they pass into the sole of the foot

2

: a fibrous band of fascia on the palm side of the wrist and base of the hand that forms the roof of the carpal tunnel and covers the tendons of the flexor muscles and the median nerve as they pass into the hand

called also transverse carpal ligament