A mathom was, according to Montgomery Scott, a useless object. In 2269, Scott, while studying the transporter process which created Spock One, beamed several mathoms toward Organia's coordinates, resulting in the creation of mirror duplicate mathoms. (TOS novel: Spock Must Die!)

The word "mathom" became obsolete when Middle English was replaced by Modern English, but was revived in the 20th century by J. R. R. Tolkien's The Lord of the Rings.
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