The only free and comprehensive online etymological dictionary of the Spanish language
sentar (Verb) "to seat"
12th cent. From Vulgar Latin sedentare 'id.,' from sedens "seating," from sedere "to sit." Prior to the 12th cent., far more common than sentar was assentar, from Vulgar Latin *adsentare. From Proto-Italic *sizd-e/o- 'id.' From Proto-Indo-European *si̯-sd-e/o- "to be sitting." Reduplication of *sed- "to sit."
Indo-European
Romance
Asturian sentar, Portuguese sentar, Galician sentar, Catalan seure, French seoir, Italian sedere, Aromanian shed, Romanian ședea, Sardinian sèdere
Italic
Umbrian sistu "he sat down"
Balto-Slavic
Old Church Slavonic sěsti "to sit down," Russian sest' 'id.,' Czech siesti 'id.,' Polish siąść 'id.,' Slovene sẹ́sti 'id.,' Old Prussian sindants "sitting," Lithuanian sė́sti 'id.'
Hellenic
Ancient Greek ἵζειν (hízdein) "to sit down"
Indo-Iranian
Sanskrit sī́dati "to sit," Avestan hiδa- 'id.'