The term "thick-brained" is often used to describe someone who is slow-witted or lacking in intelligence. There are several synonyms that can be used to describe such a person, including "dense," "unintelligent," "stupid," "ignorant," "dull," and "dim-witted." Other related terms that can be used include "slow," "dumb," "foolish," "heedless," "hard-headed," and "obtuse." It is important to note that while these terms may be used to describe someone who is perceived as being unintelligent, they should be used with caution and respect, as intelligence is a complex and multifaceted trait that cannot simply be reduced to a single term.