SEISIN Meaning of SEISIN in English n. (also seizin) Law 1 possession of land by freehold. 2 the act of taking such possession. 3 what is so held. [ ME f. AF sesine, OF seisine, saisine (as SEIZE) ] Concise Oxford English dictionary. Краткий оксфордский словарь английского языка. 2012