friction

Short definition from Wiktionary

Noun

1. 1
   The rubbing of one object or surface against another.
2. 2
   A force that resists the relative motion or tendency to such motion of two bodies in contact.
3. 3
   Massage of the body to restore circulation.
4. 4
   Conflict, as between persons having dissimilar ideas or interests; clash.
5. 5
   (Second Sino-Japanese War) Conflict, as between the Communists and non-Hanjian Kuomintang forces.