Producing or filled with steam; actively steaming or emitting steam.
From a- prefix (meaning 'in a state of') plus steam. This is a directional or state-descriptive prefix common in English that creates adjectives describing condition.
When something is asteam, it's literally billowing with steam—and this word is a perfect example of how English prefixes let us describe states; you might say a cup of tea is 'asteam' while a cold glass of water is not, and the prefix does all the work.
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