The collection of words initially acquired by a child, also known as "core vocabulary." This collection is built of words which refer most directly to the objects and speech the child is most often brought into contact with: the child's first world is a simple one and the words it acquires are those with the most direct connection to experience. Its development is motivated by a child's need to perceive, act, and speak.
Thus, the primitive vocabulary is made up of words learned by experience, as opposed to by definition. For example, an adult might say "I live in a high-rise apartment building," wheras one with a more primitive vocabulary might say "I live in a tall building with lots of other people."
Tables of words that are considered part of the primitive vocabulary are available at http://www.percepp.demon.co.uk/primvoc.htm.