Synonyms:
rudiment
Meaning: the remains of a body part that was functional at an earlier stage of life; "Meckel's diverticulum is the rudiment of the embryonic yolk sac"
Synonyms:
rudiment, first_rudiment, first_principle, alphabet, ABC, ABC's, ABCs
Meaning: the elementary stages of any subject (usually plural); "he mastered only the rudiments of geometry"