Uterine is an adjective meaning 'of the uterus' — the uterus being the organ in a woman, or a female mammal, where a baby grows before it is born. It is a medical word, and it lives almost entirely inside medical writing and doctors' speech. You meet it fixed to another noun: uterine cancer, uterine lining, uterine wall, uterine contractions, uterine bleeding. It is not used on its own after 'be' — nobody says 'the problem is uterine' in ordinary talk.

The reason English has this separate adjective is worth understanding. English often keeps a plain noun from one source and takes its adjective from Latin: heart and cardiac, lung and pulmonary, womb/uterus and uterine. That is why the adjective looks unrelated to any everyday word, and why it sounds clinical. Doctors reach for it; patients say 'in the womb' or 'in the uterus'. Say it 'YOO-ter-in' — the last part rhymes with 'in', though you will also hear 'YOO-ter-ine' rhyming with 'wine'.

Though actually, there is a second, much rarer use that surprises people. In old legal and genealogical writing, 'uterine' describes brothers and sisters who share the same mother but have different fathers — uterine siblings, as opposed to 'consanguine' ones who share a father. It comes straight from the Latin sense 'born of the same mother'. You will only see this in law books, family histories, and translations of old documents, but it explains the word's shape.