rudiment
1. [ noun ] the elementary stages of any subject (usually plural)
Synonyms: abc abc's abcs alphabet first_rudiment first_principle
Examples:

"he mastered the rudiments of geometry"

Related terms: fundamentals plural
2. [ noun ] (zoology) the remains of a body part that was functional at an earlier stage of life
Examples:

"Meckel's diverticulum is the rudiment of the embryonic yolk sac"

Related terms: body_part
Similar spelling:   rudiments
  rudimentary