noun

• (physics) A force that resists the relative motion or tendency to such motion of two bodies in contact.
  "Secondly, When a body is once in motion it will continue to move forever, unless something stops it. When a ball is struck on the surface of the earth, the friction of the earth and the resistance of the air soon stop its motion."
• (medicine, obsolete, countable) Massage of the body to restore circulation.
  "The frictions should at first be very gentle, and performed with a view to restore heat, and not to force the blood towards the heart, which in drowned persons is already too much distended with it."
• (figuratively) Conflict, as between persons having dissimilar ideas or interests; clash.
  "Thais have been watching for signs of friction between the armed forces and the monarchy—the country's two biggest sources of political power—since the death in October of Bhumibol Adulyadej, King Vajiralongkorn's long-reigning father."
• (China, historical) (Second Sino-Japanese War) Conflict, as between the Communists and non-Hanjian Kuomintang forces.