- 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. 2018
Examples from the Web for 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.
- one of the four principal phases of the moon, occurring between full moon and new moon, when half the lighted surface is visibleCompare first quarter