That's even a little stranger, as it says Thinnig instead of Thinning.
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Just a typo made by german typesetter setting up something in a language he didnt speak.
There is no german word for thinning that looks remotely like that or ending that way, besides its a verb used like an adjective in this example, ie a participle.
Regards,
Neil
It reminds me of something you use to back butter when you tile.