IPA: //ʌnˈlɛtərd//
KK: /ʌnˈlɛtərd/
Not able to read or write; lacking education or knowledge from books.
Many people in the past were unlettered and could not read or write.
Unlettered → It is formed from "un-" (meaning not) and "lettered" (from the Old English "leornian", meaning to learn or to read). The word "unlettered" means not having learned to read or write, or being illiterate.
Think of 'not' ('un-') being able to 'read or learn' ('lettered') — that's why unlettered means not being able to read.