part of speech: noun

Definition: A powerful synthetic oestrogen used in hormone therapy, as a post-coital contraceptive, and as a growth-promoting agent for livestock.

source: Oxford dictionaries

Found in “The Child Bearers” by Anne Sexton, line 6

”mine pushed into gnawing a stilbestrol cancer”

I first thought Stilbestrol was some sort of cancer as it was used as a descriptive in the line, but knowing it was a type of contraceptive gives this line a new albeit equally as grim context.