éṣṭeb - to be straight (Morris 2012:485; CSOL I 655; CSOL II 588; Bulakh 2024:204)

PWS
*ṣwb - to be fitting (SEDonline)

One wonders whether PWS *wṣb/*nṣb ‘to stand, to be erect; to be firm, stable’ may be further related as variant roots.