What is "bitter principle"

Principle \Prin"ci*ple\, n. [F. principe, L. principium beginning, foundation, fr. princeps, -cipis. See Prince.]

1. Beginning; commencement. [Obs.]

   Doubting sad end of principle unsound.
   --Spenser.

2. A source, or origin; that from which anything proceeds; fundamental substance or energy; primordial substance; ultimate element, or cause.

   The soul of man is an active principle.
   --Tillotson.

3. An original faculty or endowment.

   Nature in your principles hath set [benignity].
   --Chaucer.

   Those active principles whose direct and ultimate object is the communication either of enjoyment or suffering.
   --Stewart.

4. A fundamental truth; a comprehensive law or doctrine, from which others are derived, or on which others are founded; a general truth; an elementary proposition; a maxim; an axiom; a postulate.

   Therefore, leaving the principles of the doctrine of Christ, let us go on unto perfection.
   --Heb. vi. 1.

   A good principle, not rightly understood, may prove as hurtful as a bad.
   --Milton.

5. A settled rule of action; a governing law of conduct; an opinion or belief which exercises a directing influence on the life and behavior; a rule (usually, a right rule) of conduct consistently directing one's actions; as, a person of no principle.

   All kinds of dishonesty destroy our pretenses to an honest principle of mind.
   --Law.

6. (Chem.) Any original inherent constituent which characterizes a substance, or gives it its essential properties, and which can usually be separated by analysis; -- applied especially to drugs, plant extracts, etc.

   Cathartine is the bitter, purgative principle of senna.
   --Gregory.

   Bitter principle, Principle of contradiction, etc. See under Bitter, Contradiction, etc.

n. any one of several hundred compounds having a bitter taste; not admitting of chemical classification