空穴來風

Etymology
From 《》 by :

Note: the historical usage of the idiom may be etymologically unrelated to the mainstream usage today.

Idiom

 * 1)  to be not completely unsound; to have a basis for its existence
 * 2)  to be completely unsound; to be utterly baseless

Usage notes
This term can both mean "to be not completely unsound" and "to be completely unsound", with different dictionaries offering competing (and contradictory) definitions of the term, although in modern usage the latter definition appears more frequently. However, this latter definition is proscribed by certain media publications based on the etymology and historical usage of the term, arguing that this is a common writing mistake and that the former definition should be used instead.

Some scholars note that the ambiguous meaning of 空 in this idiom may have given rise to the contradictory definitions. For the definition of "to be not completely unsound", 空 refers to "empty", i.e. that an empty hole easily gives rise to wind, implying that a rumour has reason to have arisen. For the definition of "to be completely unsound", 空 refers to "none", i.e. that no hole exists which could have given rise to wind, implying that a rumour has no reason to arise and has been fabricated from nothing. Thus, 空穴來風 should not be viewed as a single lemma but as two separate idioms (perhaps with separate etymologies) with the same written form (同形詞). Others argue that this is an instance where misunderstanding and mistaken use of the original idiom has displaced the intended definition to become the mainstream use.

From its 6th edition, 《現代漢語詞典》 (Dictionary of Contemporary Chinese) records both meanings under its entry for 空穴來風. Prior editions had only recorded the definition "to be completely unsound".