The word "unicum" can be used to describe something that is unique or one of a kind. However, if you are looking to vary your vocabulary, there are many synonyms available to use. Some alternative words to "unicum" include "singular," "distinct," "unusual," "peculiar," "rare," "exceptional," "incomparable," "extraordinary," "original," "individual," and "idiosyncratic." All of these words convey the idea of something that is uncommon or unique. Experimenting with different synonyms will enrich your language and give you more options to convey your thoughts and ideas.