quassia
  Tropical American shrub (Quassia amara) with bright scarlet flowers.  A
  bitter substance from its wood is used in medicine and as an
  insecticide.

Queen of the meadow (Meadowsweet)
  European herbaceous plant (Spiraea Ulmaria).  North American shrubs
  (Spiraea alba or S. latifolia) having umbel-shaped clusters of white
  flowers.  Perennial herbs of the genus Filipendula in the rose family.

quinine
  Bitter, colorless, powder or crystalline alkaloid, C20H24N2O2-3H2O,
  derived from cinchona barks and used to treat malaria.

quince
  Western Asian shrub or tree (Cydonia oblonga) with white flowers and
  hard apple-like fruit.

quinsy
  Acute inflammation of the tonsils and surrounding tissue, often leading
  to an abscess.

rabies
  see hydrophobia

ranunculus bulbosus
  Perennial Old World buttercup with yellow flowers in late spring to
  early summer.

red precipitate
  Mercuric oxide (HgO) a heavy red crystalline powder formed by heating
  mercuric nitrate, or by heating mercury in the air.

repousse
  Ornamented with patterns in relief made by pressing or hammering on the
  reverse side;

resorcinol (resorcin)
  White crystalline compound, C6H4(Oh)2, used to treat certain skin
  diseases and in dyes, resin adhesives, and pharmaceuticals.

Rhamnus Purshiana (Cascara buckthorn )
  Buckthorn of the Pacific coast of the United States, which yields
  cascara sagrada.

rhatany
  Dried root of South American shrubs (Krameria lappacea or K. argentea)
  used as an astringent and in toothpaste and mouthwash.

rheumatic fever
  Acute inflammatory disease occurring after an infection from group A
  streptococci, marked by fever and joint pain.  Associated with
  polyarthritis, Sydenham’s chorea, and endocarditis; frequently causes
  scarring of the heart valves.

rheumatism
  Painful disorder of the joints or muscles or connective tissues.  Chronic
  auto-immune disease with inflammation of the joints and marked
  deformities.

rhus
  Genus of vines and shrubs including poison ivy, poison oak, and poison
  sumac.

rickets (rachitis)
  Childhood disease caused by a lack of vitamin D or calcium and from
  insufficient exposure to sunlight, characterized by defective bone
  growth.

Rochelle salts
  Potassium sodium tartrate; colorless efflorescent crystalline compound,
  KNaC4H4O6.4H2O, used in making mirrors, in electronics, and as a
  laxative

ruche
  Ruffle or pleat of lace, muslin, or other fine fabric used to trim
  women’s garments.

rumex Crispus (chrysophanic acid)
  Yellow crystalline substance found in the root of yellow dock (Rumex
  crispus).