Personally I don't think it fits, as sorcery isn't a central theme to Dominion,
Well, it's not about the 'sorcery' meaning
"Cantrip" made sense in Magic both thematically AND in game-play. Most cards are a spell of some sort, so it makes sense to have a card with a small effect be named with a word that means a small bit of magical trickery. It's quite a good name, really. Kudos to whoever coined its MtG usage.
As you infer, to use the word in Dominion we reference the in-game effect rather than the thematic meaning. But is the theme of Dominion so nebulous that we can't come up with something better than a ripoff from another game or a term that many associate with p e n 1 s pills and 419 scams?
You can send spam without thinking about it. You'll (almost) never be worse off.
Indeed many people's machines are sending spam as we speak without them thinking one ms about it.
Of the terms I've heard so far, I like "serial" the best.