critical year in one's life; inauspicious year
Refers to the main year of a person's 厄年 (やくどし), a traditional belief that certain ages bring bad luck or calamity. For men, it is typically ages 25, 42, and 61; for women, 19, 33, and 37, with 本厄 being the central, most dangerous year among the three-year period (前厄, 本厄, 後厄).
See also: 厄年
今年は本厄だから、お祓いに行こうと思う。
Since this year is my main inauspicious year, I'm thinking of going for a purification ritual.
本厄の年には、神社で厄除けの祈祷をしてもらう人が多い。
In the main inauspicious year, many people have a prayer for warding off evil performed at a shrine.