rudiment

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A fundamental element, principle, or skill, as of a field of learning. Often used in the plural.
2. n. Something in an incipient or undeveloped form. Often used in the plural: the rudiments of social behavior in children; the rudiments of a plan of action.
3. n. Biology An imperfectly or incompletely developed organ or part.

Century Dictionary and Cyclopedia

1. n. Anything which is in an undeveloped state; the principle which lies at the beginning or bottom of any development; an unformed or unfinished beginning.
2. n. An element or first principle of any art or science; especially, in the plural, the beginning, first steps, or introduction to any branch of knowledge; the elements or elementary notions.
3. n. In biology: That which is rudimentary; that which is in its first or an early stage of development, which may or may not be continued; the beginning or foundation of any part or organ: as, the rudiment of the embryo which is to go on to maturity; the rudiment of an organ whose further development has been arrested or aborted
4. n. That which is vestigial; a vestigial or aborted part, organ, or structure; an abortion; a vestige. Synonyms Fetus, Germ, etc. See embryo.
5. To furnish with first principles or rules; ground; settle in first principles.

Wiktionary

1. n. A fundamental principle or skill, especially in a field of learning (often in the plural).
2. n. Something in an undeveloped form (often in the plural)
3. n. A body part that no longer has a function
4. n. In percussion, one of a selection of basic drum patterns learned as an exercise.

GNU Webster's 1913

1. n. That which is unformed or undeveloped; the principle which lies at the bottom of any development; an unfinished beginning.
2. n. Hence, an element or first principle of any art or science; a beginning of any knowledge; a first step.
3. n. An imperfect organ or part, or one which is never developed.
4. v. To furnish with first principles or rules; to insrtuct in the rudiments.

WordNet 3.0

1. n. the remains of a body part that was functional at an earlier stage of life
2. n. the elementary stages of any subject (usually plural)