die-off
1 of 2noun
ˈdī-ˌȯf 
: a sudden sharp decline of a population of animals or plants that is not caused directly by human activity
die off
2 of 2verb
ˈdī-ˈȯf
died off; dying off; dies off
intransitive verb
: to die sequentially either singly or in numbers so that the total number is greatly diminished
Word History
First Known Use
Noun
1936, in the meaning defined above
Verb
1697, in the meaning defined above