[JadeNB]

Something can be held fast, but I don't think it is usual English to say that something fixed is fast.

Garnishment of wages is garnisheeing, though here I'll agree "garnishing" seems to be acceptable too.

[rout39574]

Something "made fast" is perfectly reasonable usage for tying it in place.

[Riseed]

Yep. And something "made fast" is also perfectly reasonable usage for vastly upgrading its speed. "Fast" can absolutely be a contronym.

[wolfram74]

I think two-word contranyms are more concrete, like "fight together".

Oversight is a less ambiguous example of a single-word contranym.

[benwills]

I've heard "fast" as a contranym to "moving quickly," referenced as "to fast" or "fasting." ie: not eating at all.

Edited to add: Sticking with the context of food, "fasting from food" contradicts someone being a "fast eater."

[riehwvfbk]

"Fasten your seatbelt" doesn't usually mean "twirl it wildly above your head".