- size of the workforce has been trebled.
- size of the workforce has been tripled.
Can they be used interchangeably?Is this an English versus American thing?
I saw trebled used in this article.
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Triple and treble are etymological twins, that is they have different phonological forms but the same etymological root.
In your example, according to their usage as intransitive verbs to be or become three times as great in number or amount they are interchangeable.
Yet there are specific contexts in which they have particular meaning such as in music, sports, places, transportation, science and technology, etc. where they cannot be used interchangeable.
The answer is right here:
Basically what they are saying is that Americans use "triple" as a verb, adjective, and noun, while British and Australians use "treble" as a verb and "triple" as a noun and adjective.