Not often seen or not often happening. It is the everyday opposite of common, and it is a gentler, more careful word than rare. If you say a bird is rare, you suggest there are very few of them left; if you say it is uncommon, you only mean you do not see it often. Teachers, doctors, and writers like this word because it does not exaggerate. You will very often meet it in the negative — 'not uncommon' — which is a polite English way of saying 'this happens quite a lot, actually': 'It is not uncommon for students to feel nervous before the exam.' Two negatives, but the meaning is positive, and it sounds calmer and more educated than 'many students feel nervous'. There is a second, older sense: unusually good or striking, as in 'a woman of uncommon intelligence'. That one is formal and now sounds a little literary; you will meet it in books more than in speech. Old writers also used uncommon as an adverb meaning 'unusually' ('uncommon good beer'), but that is now dialect or very old-fashioned, and students should not copy it.