Main Entry: pro·ges·ter·one

Pronunciation: \prō-ˈjes-tə-ˌrōn\

Function: noun

: a female steroid sex hormone C₂₁H₃₀O₂ that is secreted by the corpus luteum to prepare the endometrium for implantation and later by the placenta during pregnancy to prevent rejection of the developing embryo or fetus ; also : a synthetic steroid resembling progesterone in action