Proto-Indo-European Roots

Root/Stem: *sed-
Meanings:  to sit
Cognates (63): Greek 'ezomai (hedzomai) - with the initial s- disappearing, the same in 'izw (I make smb sit)
Latin sedeo (I sit), sedere (to sit), > 
Catalan assentarse, Spanish sentarse, Occitan asseire, French asseoir, Portuguese assentado, Aromanian sedu (I sit), Sardinian sezzere (to sit), Romanian sedea, Ladin sezzer, Italian sedere
Common Celtic *sed- (to sit), *sodion (a seat) > 
Old Irish suidim (I sit), Irish & Scottish Gaelic suidh (sit!), Manx Gaelic soie, Welsh seddu, sedd, Breton azeza
Common Germanic *sit- (to sit), > 
Gothic sitan (to sit), Old English sittan, Old Swedish sittian, Old Norse sitja, Old Frankish sitta, Old High German sizzan, > 
Swedish sitta, German sitzen, Icelandic sitja, Norwegian sitte, Danish sidde, Faroese sita, Frisian sitte, Dutch zitten
Avestan hidaiti (he is sitting) 
Tadjik sistan, nisastan (to sit), Persian neshastan, Wakhi nezd, Baluchi nishta, Waziri nostai, Pashto ksenastel
Sanskrit sidati (he is sitting), asandi (a seat) 
Takitaki sidom (I sit)
Common Baltic *séd- (to sit), > 
Lithuanian se.de.ti (to sit), Latvian sédét, Old Prussian sídons (sitting), Sudovian séstun (to sit)
Common Slavic *sédeti (to be sitting), *sesti (to sit down), > 
Ukrainian siditi (to sit), Belorussian sidzec', Old Church Slavonic sédéti, Bulgarian sedja (I sit), Macedonian sedam, Serbo-Croatian sjediti (to sit), Slovene sedeti, Czech sedéti, Slovak sediet', Polish siedziec', Upper Sorbian sedzec', Lower Sorbian sejzes', Russian sidet' (to sit), sizhu (I sit).
Armenian nusdel (to sit), from *nu-sidel
Notes: The stem was considered by Gamkrelidze & Ivanov as an "inactive" one, i.e. it was used in Proto-Indo-European only with inanimate nouns, denoting things, but not people. Later, when languages lost that distinction between active and inactive words, the stem became normal in the majority of languages. However, several languages showed another stem, which is believed to have been used for "active" nouns. Hittite, for example, has es'zi (he sits), the same for a few other languages. So the active stem with this meaning was *es-
This opposition of active - inactive verbs is one of the most prominent theories in IE linguistics.