From an unused root meaning to estop; the stocks -- stocks.
Englishman's Concordance
1) stocks (for feet) Part of Speech: noun masculine A Related Word by BDB/Strong’s Number: from an unused root meaning to estop Same Word by TWOT Number: 1464
Brown-Driver-Briggs
סַדnoun [masculine]stocks, for confining feet of culprits (probably loan-word from Aramaic סַדָּא, סַדָּנָא; Late Hebrew סַד, plural סַדִּין);=Latin nervus, Greek ποδοκάκη; — absolute רַגְלַיִם׳שִׂים בַּמּJob 13:27 (ᵐ5κώλύμα), Job 33:11 (ᵑ6ξύλό); (compare synonym מַהְמֶּכֶת, and Greek equivalent there cited).
Englishman's Concordance (References)
Strong's Hebrew: 5465. סַד (sad) — 2 Occurrences
Job 13:27 HEB: וְתָ֘שֵׂ֤ם בַּסַּ֨ד ׀ רַגְלַ֗י וְתִשְׁמ֥וֹר NAS: my feet in the stocks And watch KJV: my feet also in the stocks, and lookest narrowly INT: put the stocks my feet and watch
Job 33:11 HEB: יָשֵׂ֣ם בַּסַּ֣ד רַגְלָ֑י יִ֝שְׁמֹ֗ר NAS: my feet in the stocks; He watches KJV: my feet in the stocks, he marketh INT: puts the stocks my feet watches