Rudiment, usually used in the plural, means the basics. If you know the alphabet, you have the rudiments of reading at your disposal.
You might learn the rudiments of cooking from your mother, but you won’t become an expert until you spend time in your own kitchen. In biology, the word rudiment means an undeveloped part of an organ or limb, like you would find in an embryo or fetus.
the elementary stages of any subject (usually plural)
the remains of a body part that was functional at an earlier stage of life