Dictionary.com
definitions

arc cos

  1. arc cosine.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for arccos

arccos

abbreviation for
  1. arc-cosine: the function the value of which for a given argument between –1 and 1 is the angle in radians (between 0 and π), the cosine of which is that argument: the inverse of the cosine function
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012