乃
nǎi HSK7

then

乃 nǎi
to be verb
to be; equivalent to the copula 是 shì

失败乃成功之母。

shī​bài nǎi chéng​gōng zhī mǔ.

Failure is the mother of success.

only verb
only; not until; used to indicate that something happens only at a specific time or under a specific condition

此时乃悟其意。

cǐ​shí nǎi wù qí yì.

It was only then that I understood his intention.

thus verb
thus; so; therefore; then; thereupon; used to indicate a logical sequence or consequence

闻其名，乃知其人。

wén qí míng, nǎi zhī qí rén.

By hearing the name, one knows the person.

Frequency
Character
Written text
1,165th most common 121.5 per million
Movie subtitles
2,296th most common 12.1 per million appears in 3% of films
Word
Movie subtitles
4.77 per million appears in 1% of films
Written text
41.4 per million

Details
HSK 3.0
Level 7
Strokes
2
Unicode
U+4E43

Sources
Definitions
CC-CEDICT
Frequency data
MTSU Chinese text computingSUBTLEX-CHBCC Corpus (BLCU)