strapless
n.a piece of clothing, like a dress or a bra, that does not have any straps to hold it up. It stays in place by the weight of the fabric or by a band around the body.
n.a garment or undergarment lacking shoulder straps for support. Often used to describe styles that rely on a wide band or the weight of the fabric to remain in place.
“She wore a beautiful strapless dress to the wedding.”
“The designer created a collection of strapless evening gowns that relied on intricate beading to keep the fabric secure.”
“While strapless styles were once considered too revealing for formal occasions, they have since become a staple of modern evening wear, often paired with a matching bra for added support.”
From strap + -less. The noun sense is by analogy of strap-on.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.