乃
nǎi · HSK 7
therefore
nǎi sounds like nigh — therefore the end is nigh
乃 is a literary connector meaning therefore or thus. Lock the sound to the near-homophone nigh: the conclusion follows, therefore the end is nigh.
乃 — single component, derived from a pictograph
乃 originated as a pictograph, traditionally interpreted as depicting a curved or twisted form, possibly a breath or rope. Over time it lost concrete meaning and became a function word used as a pronoun ('you') in classical Chinese and as an adverb meaning 'thereupon' or 'then'.