Succussion (apparently from the Latin verb succutere, from sub- ‘away’ + quatere ‘to shake’) was a diagnostic method mentioned by Hippocrates in which you shake a person vigorously and listen to the sounds in the chest (e.g. The Cyclopædia of Practical Medicine: Comprising Treatises on the Nature ... - Google Books).
When homeopathy was invented by Hahnemann, he adopted the term:
The higher we carry the attenuation accompanied by dynamization (by two succussion strokes), with so much the more rapid and penetrating action does the preparation seem to affect the vital force and to alter the health, with but slight diminution of strength even when this operation is carried very far…
(Aphorism 287 of the fifth edition of The Organon of Healing)
It’s now used almost exclusively in that context. It is a practice where a vial containing water in which an irritant has been diluted is either shaken vigorously or subjected to a shock, like smacking it against a table. Practitioners believe it enables the water to retain a memory of the substance; the idea that water retains a memory of things it encounters was so influential that it became a plot point in the movie Frozen 2.
The word “succuss” is not in the databse.