active principle n.
A constituent of a drug, usually an alkaloid or glycoside, on which the characteristic therapeutic action of the substance largely depends.
Is it used by nerves as food, or used by lungs, heart, or any organ as an active principle in the magnetic or electric forces?
The active principle of the seeds has not been satisfactorily isolated.
If celery seed has any active principle it has never been isolated.
It has been the blessing of France; it was its active principle down to 1820.
The active principle seems to be filicic acid and the ethereal oil.
Down under the sod this active principle of life is still at work.
The passive principle is pure matter without qualities; the active principle is reason, or God.
The nature of the active principle of aconite root does not appear to have been satisfactorily determined.
It contains a substance called Aloetine, which some regard as its active principle.
What is the active principle of your 'sevens'—or haven't you figured it out?