1. rudiment - Noun
2. rudiment - Verb
That which is unformed or undeveloped; the principle which lies at the bottom of any development; an unfinished beginning.
Hence, an element or first principle of any art or science; a beginning of any knowledge; a first step.
An imperfect organ or part, or one which is never developed.
To furnish with first principles or rules; to insrtuct in the rudiments.
Source: Webster's dictionaryMeckel's diverticulum is the rudiment of the embryonic yolk sac Source: Internet