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to chip; to be chipped; to break (off); to be damaged
to be missing (from a set, team, etc.); to be absent; to become lost
to be lacking (in); to be short (of); to be deficient; to be wanting (in)
to wane (of the moon); to go into eclipse
コップが闕けてしまった。
The cup got chipped.
知識が闕けていると感じる。
I feel I'm lacking knowledge.
月が闕けてきましたよね。
The moon is waning.