In Jainism:

• Every Arihant is a Kevalī (Keval‑jñānī).

Arihant = a soul who has destroyed the four ghāti karmas and has attained Keval‑jñāna (omniscience) while still in a body.

• But every Keval‑jñānī is, by definition, an Arihant.

As soon as a soul attains Keval‑jñāna, it becomes an Arihant (also called Kevalī). When that embodied life ends, the same soul becomes a Siddha (fully liberated, without body).

So, in simple English: If someone has Keval‑jñāna, they are an Arihant (till death). After death, they are no longer called Arihant; they are called Siddha.