This is the 12018th most frequent Russian word.
зенитными
"Zenitnymi" means "anti-aircraft" or "relating to zenith."
Here, 'зенитными' is used as an adjective describing the systems that are designed for anti-aircraft purposes.
Зенитными системами мы защищаем наше небо.
We defend our skies with anti-aircraft systems.
In this sentence, 'зенитные' is qualifying the complexes as anti-aircraft systems.
Военные разместили новые зенитные комплексы на границе.
The military deployed new anti-aircraft complexes at the border.
On this occasion, 'зенитных' describes the missiles as being designed for anti-aircraft operations.