Simpletonian is a term often used to describe someone who is considered foolish or lacking intelligence. Synonyms for this word include dimwit, nincompoop, imbecile, dumbbell, fool, ignoramus, dolt, and dunce. These words all have similar connotations and can be used interchangeably when describing someone who lacks knowledge or common sense. It is important to use these words with caution, as they can be considered insulting or offensive in certain situations. When looking for a more polite term to describe someone who is not very intelligent, consider using words like naive, unsophisticated, or inexperienced.