(small) dust, powder

Boyd’s Bible Dictionary:

(storm breath). Symbol of mourning (Josh. 7:6; Isa. 47:1); feebleness (Gen. 18:27; Job 30:19); countless numbers (Gen. 13:16); low condition (1 Sam. 2:8); rage (2 Sam. 16:13; Acts 22:23); renunciation (Matt. 10:14; Mark 6:11; Acts 13:51). A sand storm (Deut. 28:24).

Concise Bible Dictionary:

Small particles of matter found on the ground, out of which man was formed, to whom it was said, “Dust thou art, and unto dust shalt thou return” (Gen. 2:7; Gen. 3:19). “The first man is of the earth, earthy” (1 Cor. 15:47). It is used as a symbol of weakness: “he remembereth that we are dust” (Psa. 103:14). To “lick the dust” is figurative of defeat (Psa. 72:9). To “cast dust upon the head” was a sign of grief (Ezek. 27:30; Rev. 18:19). To “shake the dust off the feet” on leaving a city where the servants of Christ had been rejected, was leaving them to judgment: not even the dust of their city should be presented before the messengers’ Master (Matt. 10:14; Acts 13:51). Similarly dust was cast or shaken into the air by men in great indignation (Acts 22:23).

Strong’s Dictionary of Hebrew Words:

from root of 79; light particles (as volatile)
KJV Usage:
(small) dust, powder