mukou
無劫 (mukou) is the Japanese go term for a false ko threat.
In this diagram, is mukou.
If White plays at a after Black fills the ko, then Black can play b, White c, and then Black d.
What is the source of this word?
What would its characters be? The "o" in "kou" let's me drop-off Japanese as candidate.
With the given explanation, "Mu" let's me associate with "Wu" and "mu" in Chinese:
无, resp. 無 wú ; negative, no, not; lack, have no
莫 mò mù (do not, is not, can not; negative)
牟 móu mù (make; seek, get; barley; low)
目 mù, (eye, point in Go)
What could the "kou" be?
Bob McGuigan: The term is Japanese. Mu is 無 (negation) and kou is 劫 . In Japanese the vowel is elongated as in kou even though it is usually spelled ko in western languages. By the way, one of the meanings of the kanji 劫 (kou) is "threat".