This is the 8367th most frequent Japanese word.
必定
"必定" means "inevitability" or "certainty."
In this sentence, "必定" is used to express that effort is a necessary condition for achieving success.
成功するためには努力が必定です。
Effort is essential for success.
Here, "必定" conveys the idea of an event being certain or unavoidable due to circumstances.
彼が来るのは必定と思われる。
It seems inevitable that he will come.
In this example, "必定" means a logical inevitability or conclusion derived from observed facts.