ru·di·ment 
(rdə-mənt)
(rdə-mənt)n.
1. often rudiments
a. A fundamental element, principle, or skill, as of a field of learning: the rudiments of calculus.
b. Something in an incipient or undeveloped form: the rudiments of social behavior in children; the rudiments of a plan of action.
2. Biology An imperfectly or incompletely developed organ or part.
[Latin rudīmentum, from rudis, rough, unformed.]
ru′di·mental (-mĕntl) adj.