What does "brassiere" mean?

Dated form of bra (“item of underwear”).

What is a synonym for "brassiere"?

Common synonyms include: bra, advocate, alpenstock, arm, athletic supporter, back.

/bɹəˈzɪɚ/ noun

noun ·Uncommon ·College level

Noun

1
Dated form of bra (“item of underwear”). alt-of, dated
"She started to strap her brassiere over her breasts."
2
an undergarment worn by women to support their breasts wordnet

"At the end of a long day she would remove her brassiere and settle into more comfortable clothing."

Borrowed from French brassière. Doublet of brachiaria.