the instant, approximately one week after a full moon, when half of the moon's disk is illuminated by the sun.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for last quarter
Historical Examples of last quarter
A last-quarter moon was now shining low on the eastern horizon.
The last-quarter moon rose at long last, and shone upon the glassy-rippled water of the lagoon.
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