underpopulation means insufficient population. Lexicurio rates it Sui generis — a strength score of 87 out of 100.
Etymology
From under- + population.
noun
- Insufficient population.““Panicology” considers the evidence on both sides of a large number of worries that have beset the industrialized world in modern times, including the “population crisis” (now one of underpopulation that threatens the wealth and health of aging populations in countries like Italy and Russia)[…]”