Atypical means not typical: not the usual kind, not the pattern you expect. A typical Monday is ordinary; an atypical Monday has something odd in it. The word is a little formal. Doctors use it a lot: atypical signs do not match the usual picture of an illness. In everyday talk, unusual, not typical, or a bit different often do the same job, and they sound warmer. Though actually, unusual is a bit wider. Unusual just means 'not common'. Atypical quietly points at a pattern first, then steps outside it. Calling a person atypical can sound like a file note — cold, as if they were a sample — so be gentle there. Scientists and teachers also use it for results that do not follow the common pattern.