The term 'most astucious' may be tough to relate to antonyms directly, as it is a rather rare word. However, the definition of astucious is 'shrewd or crafty', and we can assume that the antonyms of astucious would be words that describe the opposite characteristics. Words such as 'naive', 'gullible', 'unsuspecting' and 'ingenuous' could be considered antonyms. Other words like 'honest', 'straightforward', 'frank', and 'open' can also be related to the opposite of astucious. To use antonyms effectively, it is best to identify the context in which they should function, which can help to create meaning and relevance in a sentence or situation.