*aitaz

From Proto-Indo-European *h₂óyd-o-s, an o-grade thematic noun from root *h₂eyd-, thus originally ‘swelling, tumor’ and secondarily ‘ulcer, abscess’. The formation is closely paralleled semantically by Ancient Greek οἶδος (oîdos) and belongs with οἰδέω (oidéō) and Old Armenian այտնում (aytnum); compare also Latin aemidus (Beekes 2010: 1053–54; Kroonen 2013: 14; Martirosyan 2010: 61, 706; Orel 2003: 10). The same root underlies *aitrą < *h₂eyd-ro-m (and probably *aistô), reflecting a wider semantic development from ‘swelling’ to ‘tumor, pustule’ and thence ‘pus, poison’. A Balto-Slavic connection has also been proposed, especially Old Church Slavonic ядъ (jadъ) < Proto-Slavic *jadъ, although the precise preform and relationship are less secure; more recent discussion continues to associate this group with *h₂eyd- (Matasović 2022: 12).