From Wiktionary, the free dictionary
By surface analysis, седя́ (sedjá, “to be sitting”) + -еж (-ež).
седе́ж • (sedéž) m
- act of sitting
- sitting posture
- сяд (sjad, “seat”) (dialectal)
- “седеж”, in Речник на българския език [Dictionary of the Bulgarian Language] (in Bulgarian), Sofia: Bulgarian Academy of Sciences, 2014
- “седеж”, in Речник на българския език [Dictionary of the Bulgarian Language] (in Bulgarian), Chitanka, 2010