n.
Pronunciation: - ' pir- ē - ə d
Function: noun
Date: 1920
: a recurring cycle of light and dark periods of constant length also : PHOTOPHASE 2
– pho · to · pe · ri · od · ic \ - ˌ pir- ē - ' ä-dik \ adjective
– pho · to · pe · ri · od · i · cal · ly \ -di-k( ə -)l ē \ adverb