A boat neckline refers to a style of neckline in clothing that is wide and scoops across the collarbone like the shape of a boat's hull. Full definition
Full length sleeve and modern high boat neckline in front. (elizabethdye.com)
I love the wide boat neckline, it's so flattering and ready for accessories. (notdeadyetstyle.com)
Crafted from a lightweight fabric with a touch of stretch for comfort, this piece features an elegant boat neckline, cap sleeves and a relaxed shape through the body. (kelkoo.co.uk)