Today's word

plastron \PLASS-trun\ - 1a. a metal breastplate formerly worn under the hauberk  b. a quilted pad worn in fencing practice to protect the chest, waist, and the side on which the weapon is held  2. the ventral part of the shell of a tortoise or turtle  3a. a trimming like a bib for a woman's dress  b. a man's separate or detachable shirtfront

The second definition was provided in the WOTD quick link on the  home page, so I guessed that maybe the other senses of this (new, for me) word developed from this one. The full write-up says otherwise.