Impossible to prevent or to get around; it is going to happen and nothing you do will stop it. It sits with things people would rather not have — delays, costs, accidents, conflict, death — so it usually comes with a small sigh. Two uses are worth separating. First, the plain one: 'the delay was unavoidable', meaning nobody could have prevented it. Second, and very common at work, it is used as a polite defence: when a manager says 'these job cuts are unavoidable', they are saying 'do not blame me, there was no other road'. Listeners often disagree, which is why you also hear 'nothing is unavoidable'. There is a set phrase worth learning whole: 'unavoidable circumstances' — the standard formal reason given for a cancellation. Compare 'inevitable', which is close but points forward at what is certain to come, often with a feeling of fate; 'unavoidable' points at a thing already in your path that you cannot step around.