From an unused root meaning to estop; the stocks -- stocks.
H5465. sad
סַד noun [masculine] stocks, for confining feet of culprits (probably loan-word from Aramaic סַדָּנָא סַדָּא, ; Late Hebrew סַד, plural סַדִּין); = Latin nervus, Greek ποδοκάκη; — absolute בַּמּ רַגְלַיִם׳שִׂים Job 13:27 (ᵐ5 κώλύμα), 33:11 (ᵑ6 ξύλό); (compare synonym מַהְמֶּכֶת, and Greek equivalent there cited).