pho·to·pe·ri·od·ism 
(fō′tō-pîrē-ə-dĭz′əm)
(fō′tō-pîrē-ə-dĭz′əm)n.
An organism's response or ability to respond to changes in photoperiod.
- blackish
- blackjack
- "Black Jack."
- black knot
- black lead
- blackleg
- black-legged tick
- black letter
- black light
- black liquor
- blacklist
- blacklister
- black locust
- black lung
- blackly
- black magic
- blackmail
- blackmailer
- Black Maria
- black market
- black-market
- black-market
- black-marketeer
- black-marketeering
- black-marketer