waning moon
second half of a lunar month, when the lit portion of the Moon seen from the Earth is shrinking, between the full moon and the next new moon
en-US/ˈweɪnɪŋ ˈmun/
en-GB/ˈweɪnɪŋ ˈmuːn/
second half of a lunar month, when the lit portion of the Moon seen from the Earth is shrinking, between the full moon and the next new moon