onset

The beginning of something, especially something unpleasant.

• (no common derivatives)

• onset of winter
• onset of disease
• sudden onset
• early onset
• onset of symptoms

1. 1.The onset of the monsoon season brought much-needed rain to the drought-stricken region. (beginning)
2. 2.Early-onset Alzheimer's disease affects people under the age of 65. (medical beginning)

• beginning/bɪˈɡɪnɪŋ/— the start — more general
• commencement/kəˈmɛnsmənt/— the start — more formal
• outbreak/ˈaʊtbreɪk/— sudden start — for disease or conflict

from on + set — the point at which something "sets on" or begins