noun
undershirt; knitted undershirt
A knitted undershirt, typically made of cotton or wool, worn as a base layer. The term is somewhat dated; modern Japanese often uses アンダーシャツ or 肌着 for general undershirts.
from Spanish medias · from Portuguese meias · from English shirt
寒い日はメリヤスシャツを着ると暖かい。
On cold days, wearing a knitted undershirt keeps you warm.
祖母はいつもメリヤスシャツを編んでくれた。
My grandmother used to knit undershirts for me.
From Spanish 'medias' or Portuguese 'meias' (stockings, knitted goods) and English 'shirt'. The exact path is uncertain, but it likely entered Japanese through trade contact, referring to a knitted shirt.