The word "thicko" is considered to be a slang term used to describe someone who is not very intelligent or perceptive. There are different synonyms for this word, including dimwit, ignoramus, fool, idiot, and simpleton. Dimwit refers to someone who lacks intelligence or common sense. Ignoramus implies lack of knowledge or information. Fool is a general term used to describe someone who is silly or stupid. Idiot is a derogatory term used to describe someone who is mentally deficient. Simpleton implies a lack of sophistication or worldly knowledge. These words can be used interchangeably with thicko and should be used with caution as they can be offensive.