Foul

Foul [Heb. rapas/mirpas, baʾash, tsakhanah, zanakh, baʾeshah; Grk. cheimōn, akathartos, kakos]. That which is bad-smelling, harmful, or unclean; to make something offensive to the senses.

The word "foul" is used in the NKJV only ten times. In the OT the Hebrew terms are mostly verbs, primarily used in the sense of making something to smell or stink. It may be an action that causes water to stink (baʾash, Exod 7:18, 21; zanakh, Isa 19:6), but also an action that simply disturbs the water and makes it muddy (rapas, Ezek 32:2; 34:18; mirpas, Ezek 34:19). Besides its association with water, the terms convey actions that cause bad smell (baʾash) that is related to dead frogs (Exod 8:14), manna (Exod 16:20), and a wound (Ps 38:5). Dead flies cause the perfumer's oil to smell (baʾash, Eccl 10:1). Nominal forms describe stink weeds (baʾeshah, Job 31:40) and the stench of decayed dead bodies of enemies (tsakhanah, Joel 2:20).

Although in the NT the idea of "foul" also carries negative connotations, it is not associated with bad smell. In Matthew 16:3, the NKJV translates cheimōn as "foul weather," the same term translated as "winter" elsewhere (Matt 24:20; John 10:22; 2 Tim 4:21) or "tempest" (Acts 27:20). In Revelation, "foul" is used symbolically in two contexts—first in the context of the first plague describing harmful and malignant sores (kakos, Rev 16:2) and then in the context of the judgment over Babylon referring to unclean spirits and birds (akathartos, Rev 18:2).