: "sey," a Scots and Ulster dialect word (written also scy, sci, si, sie, sy in glossaries) meaning ‘the opening of a gown, etc., into which the sleeve is inserted; the part of the dress between the armpit and the chest (of obscure etymology, and sometimes confused with "scythe" due to similarly curved shapes).
In the context of Scottish and Ulster dialects, "sey" refers to a specific part of a garment, namely the opening for the sleeve and the adjacent area between the armpit and chest.