Depopulator is a unique and rarely used word to describe something that reduces the population of a particular species or group. While there may not be many direct synonyms for this term, there are several similar words that can be used to convey a similar message. "Exterminator" can describe someone or something that eliminates a particular group, including pests or other unwanted creatures. "Annihilator" is a stronger term that suggests total destruction or obliteration. "Decimator" is another term that implies a significant reduction in population or numbers. All of these words can be used effectively in place of "depopulator" to convey a similar meaning.