If you don’t understand what a person means, you can’t evaluate that person’s claims or arguments. Of all the things people are ignorant of, nothing hinders critical thinking more than lack of adequate vocabulary. A quick and efficient way to overcome this block to critical thinking is to use a good dictionary, one that doesn't just provide synonyms, but provides etymology and guidance for usage. A good dictionary will not only give the various meanings a word can have, but will also give examples of the word used in different ways. Knowing the origins of words can help with understanding new words you come across that use the same prefixes, suffixes, or root words.