There's an explanation on page 36 (page 10 of the PDF file) of Pita Tan's introduction to SN 56.11. The context is explaining the various types of dukkha ("birth is dukkha, death is dukkha, ..." and so on).

When we understand this, we have a good idea why nirvana—the final state of the Buddha and the arhats—are also “described” (for the convenience of the understanding of the unawakened) as being the opposites of birth, decay, disease and death—nirvana is thus non-birth, non-decay, non-disease and nondeath, that is to say:

• ajāta or abhūta “birth-free” being unborn, being free of rebirth, hence, no redeath;

• avyādhi or ajarā “decay-free” not subject to change, bodily or mental, or disease and dis-ease;
• asoka or abhaya “fear-free” without craving, there is no fear, nor danger from the world;
• amara or amata “death-free” without rebirth, there is no redeath, the cycle is finally broken.

There's an explanation on page 36 (page 10 of the PDF file) of Pita Tan's introduction to SN 56.11. The context is explaining the various types of dukkha ("birth is dukkha, death is dukkha, ..." and so on).

When we understand this, we have a good idea why nirvana—the final state of the Buddha and the arhats—are also “described” (for the convenience of the understanding of the unawakened) as being the opposites of birth, decay, disease and death—nirvana is thus non-birth, non-decay, non-disease and nondeath, that is to say:

• ajāta or abhūta “birth-free” being unborn, being free of rebirth, hence, no redeath;

• avyādhi or ajarā “decay-free” not subject to change, bodily or mental, or disease and dis-ease;
• asoka or abhaya “fear-free” without craving, there is no fear, nor danger from the world;
• amara or amata “death-free” without rebirth, there is no redeath, the cycle is finally broken.