From BiblePortal Wikipedia

Webster's Dictionary [1]

(1): ( n.) Any one of various more or less destructive fungus diseases attacking cultivated plants, and usually forming dark-colored crustlike spots.

(2): ( n.) A disease of potatoes producing pits in their surface, caused by a minute fungus (Tiburcinia Scabies).

(3): ( v. i.) To become covered with a scab; as, the wound scabbed over.

(4): ( n.) A mean, dirty, paltry fellow.

(5): ( n.) The itch in man; also, the scurvy.

(6): ( n.) The mange, esp. when it appears on sheep.

(7): ( n.) A nickname for a workman who engages for lower wages than are fixed by the trades unions; also, for one who takes the place of a workman on a strike.

(8): ( n.) An incrustation over a sore, wound, vesicle, or pustule, formed by the drying up of the discharge from the diseased part.

(9): ( n.) A slight irregular protuberance which defaces the surface of a casting, caused by the breaking away of a part of the mold.

King James Dictionary [2]

SCAB, n. L. scabbies, scaber, rough.

1. An encrusted substance, dry and rough, formed over a sore in healing. 2. The itch or mange in horses a disease of sheep. 3. A mean, dirty paltry fellow. Low.

Wilson's Dictionary of Bible Types [3]

 Isaiah 3:17 (b) This figure is used to describe the results on the nation of Israel when GOD sends among them invading enemies, the pestilence, and the famine.

Hastings' Dictionary of the Bible [4]

SCAB . See Medicine, p. 599 b .

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [5]

( גָּרָב , Garab,  Deuteronomy 28:27; elsewhere "scurvy," a diseased Scurf on the skin; מַסְפִחִת , Mispachath,  Leviticus 13:6-8; a harmless cutaneous eruption; סִפִּחִת , Sappachath,  Leviticus 13:2 Mange in the hair causing it to fall out; kindred with these last two is שָׂפִח for סָפִח , saphach, to "smite with a scab,"  Isaiah 3:17, i.e. premature baldness; יִלֶּפֶת , Yallepheth,  Leviticus 21:20;  Leviticus 22:22, an itching or tetter in the skin). (See Disease); (See Leprosy).