Unwonted is a pretty old-fashioned word now, meaning something unusual or out of the ordinary. Nowadays, unwonted is a pretty unwonted word itself.
Unwonted was once a particularly beloved literary term, favored by authors like Henry James and Charles Dickens, whose books were filled with "unwonted circumstances," and the like. Not to be confused — as it often is — with unwanted, meaning not wanted or desired. The confusion arises not just because the words sound identical, but because their meanings overlap: it's a safe bet that anything unwonted is generally unwanted, too.