胸当て

western-style armor for the chest: a breastplate

a chest protector used in traditional Japanese firefighting

(by extension) a cloth bib or chest covering worn as protection from the sun by travelers or messengers, or as protection from food and spills by children or workers

(fashion) the front portion of an apron, jumper dress, or overalls that extends above the waist and covers the front of the body

(archery) a plastron, a chestguard, used in 弓道 (kyūdō, “traditional Japanese archery”) to protect the chest from the bowstring (more commonly, but not exclusively, used by women)

a guess, an estimate, a conjecture