“illness” in Japanese is 病, read byou, hei, yamai (びょう, へい, やまい, や). It is a Grade 3 Kyōiku kanji, taught in year 3 of Japanese elementary school, and appears in words such as 病院 (hospital).
What does 病 mean?
母が病気で休んだ。
Same sound, different character — the classic trap. Compare them side by side: