Characterized by or marked with hebetude; dull, stupid, mentally sluggish, and lacking awareness or intelligence.
From hebetude + -inous, an adjectival suffix from Latin meaning 'characterized by' or 'full of' (as in 'gelatinous' from gelatin or 'gratuitous' from gratuity). This creates a more emphatic form than just hebetic.
This is the ultimate insult word for stupid—saying someone is 'hebetudinous' sounds so scholarly and specific that it might confuse the person you're insulting, which adds a layer of irony!
Complete word intelligence in one call. Free tier — 50 lookups/day.