Most important element; SYN. main, primary, principal.

ETYM Cf. French essentiel. Related to Essence.
1. Absolutely necessary; vitally necessary; SYN. indispensable.
2. Absolutely required and not to be used up or sacrificed.
3. Basic and fundamental.
4. Being or relating to or containing the essence of a plant etc.

ETYM Cf.Latin operativus, French opératif.
1. Being in force or having or exerting force.
2. Effective; producing a desired effect; SYN. key.
3. Of or relating to a surgical operation.

ETYM French, from Latin principalis. Related to Prince.
1. Highest in rank, authority, character, importance, or degree.
2. Of or pertaining to a prince; princely.