This noun denotes foam or froth, whether from sea waves, a river, or a diseased body. Luke uses it in his account of the demon-possessed boy (Luke 9:39) who is seized by a spirit that throws him into convulsions 'with foaming' (μετὰ ἀφροῦ). The term vividly captures the physical symptoms of violent spiritual oppression—the boy's mouth froths as the unclean spirit ravages him. Classical Greek uses ἀφρός for sea foam (famously, Aphrodite born from it) and the foaming mouths of rabid animals or epileptics. Luke's clinical description underscores the brutal reality of demonic affliction, which Jesus' word instantly dispels.