night·fall 
/ˈnaɪtˌfɑ:l/ noun
/ˈnaɪtˌfɑ:l/ noun [noncount] : the time of day when the sky gets dark : the time when night begins
▪ When nightfall came, we were still waiting for the electricity to come back on. ▪ We should be back by/before nightfall. [=dark]
▪ When nightfall came, we were still waiting for the electricity to come back on. ▪ We should be back by/before nightfall. [=dark]
