rigor

Multiple Entries:
  rigor    rigour  

Concise Oxford English Dictionary © 2008 Oxford University Press:
rigor1 /ˈrɪgɔː, ˈrʌɪgɔː, -gə/

▶noun Medicine

• 1 a sudden feeling of cold accompanied by shivering and a rise in temperature, especially at the onset or height of a fever.

• 2 short for rigor mortis.

– origin ME: from L., lit. ‘stiffness’, from rigere ‘be stiff’.

Concise Oxford English Dictionary © 2008 Oxford University Press:
rigor2

▶noun US spelling of rigour.

Concise Oxford English Dictionary © 2008 Oxford University Press:
rigour /ˈrɪɡə(r)/ (US rigor)

▶noun

• 1 the quality of being rigorous.

  ■ severity or strictness.

• 2 (rigours) demanding, extreme conditions.

– origin ME: from OFr. rigour from L. rigor ‘stiffness’.