bù​débu​de

cannot

不得 bù​dé frequency
cannot verb
cannot; to be unable to; often used in set phrases like 不得而知 bù​dé'ér​zhī
must not
must not; may not; not allowed to
to not obtain
(bound form) to not obtain; to fail to get; to not receive
to not be [verbed]
(archaic) to not be [done by someone], used to indicate the passive voice
不得 bu​de
[potential] adverb
Used after a verb or adjective to express that something is impossible or not permitted.

Frequency

Movie subtitles
10.7 per million appears in 5% of films
Written text
83.3 per million

Sources