IPA: /ˈsɪk.nəs/
KK: /ˈsɪk.nəs/
A state of being unwell or having a disease, often causing discomfort or pain.
She stayed home from school because of her sickness.
Sickness → It originates from Old English 'sēoc' (meaning ill or sick) and the suffix '-ness' (meaning the state of being). The word 'sickness' refers to the state of being ill or unwell.
Think of the Old English word for being 'ill' — that's what 'sickness' means, the state of being unwell.