This is the 5683rd most frequent Japanese word.
ぜん
"ぜん" (zen) means "goodness" or "virtue" and can also refer to "Zen" in Buddhist context.
In this sentence, "全 (ぜん)" is part of "全て (すべて)", which means 'all' or 'entire.' It denotes completeness or entirety.
全ての人は平等であるべきです。
All people should be treated equally.
Here, "禅 (ぜん)" refers to Zen, a school of Buddhism focusing on meditation and self-awareness.
禅の教えは心の平和を重視します。
The teachings of Zen emphasize inner peace.
"全然 (ぜんぜん)" in this context modifies the negative adjective "面白くない" (not interesting), meaning 'not at all.'