Offhand is a word that can be used to describe a casual and unpremeditated manner. However, there are a few synonyms that can be used to convey a similar meaning. For instance, the word impromptu can be used to describe something that is done without prior planning or preparation. Similarly, the term spontaneous can be utilized to describe a situation that arises suddenly, without any forethought. Additionally, terms like casual and nonchalant can also be used to refer to an offhand manner. Other useful synonyms for the word offhand include unscripted, improvised, extemporaneous, and ad-lib. These words can be employed to evoke a sense of spontaneity and casualness in speech or writing.