ならぬ

is not

Meanings

  1. pre-noun adjectival, formal, from copular なり is not; am not; are not
  2. expression, used before nouns, formal, from 成る beyond one's power; unachievable; impossible
  3. dated, from 成る must not ...; should not ...

In sentences

行ぎょうかねばならぬ。 I must go. #13863192

人ひとは働かねばならぬ。 A man must work. #144452

ツバメ一羽いちわで夏なつにはならぬ。 One swallow does not make a summer. #202566

人ひとは足たるを知ちらねばならぬ。 People must learn to be satisfied. #382899

相手あいてがなくてはけんかにならぬ。 It takes two to make a quarrel. #140461

黒くろに黒くろをたしても白しろにはならぬ。 Two blacks do not make a white. #172985

言いうことに気きをつけねばならぬ。 You should be careful what you say. #174787

鉄てつは熱あついうちに打ダースたねばならぬ。 You must strike while the iron is hot. #391938