Early 20th century; earliest use found in Journal Massachusetts Association Boards Health. In some forms from alga + -cide; in some forms apparently originally from algae, plural of alga + -cide.
Definition of algaecide in US English:
algaecide
(also algecide, algacide)
nounˈaldʒɪsʌɪd
Algicide.
Origin
Early 20th century; earliest use found in Journal Massachusetts Association Boards Health. In some forms from alga + -cide; in some forms apparently originally from algae, plural of alga + -cide.