Strong's #8414: tohuw (pronounced to'-hoo)
 from an unused root meaning to lie waste; a desolation (of surface), i.e. desert; figuratively, a worthless thing; adverbially, in vain:--confusion, empty place, without form, nothing, (thing of) nought, vain, vanity, waste, wilderness.
Brown-Driver-Briggs Hebrew Lexicon:
 ּּ 
  tôhû 
 
 1) formlessness, confusion, unreality, emptiness
 
 1a) formlessness (of primeval earth)
 
 1a1) nothingness, empty space
 
 1b) that which is empty or unreal (of idols) (figuratively)
 1c) wasteland, wilderness (of solitary places)
 1d) place of chaos
 1e) vanity
 
  Part of Speech: noun masculine
Relation: from an unused root meaning to lie waste
Usage:
This word is used 20 times:
Genesis 1:2: "And the earth was  without form, and void; and darkness was upon the face of the deep."
Deuteronomy 32:10: "He found him in a desert land,  and in the waste howling wilderness; he led him about, he instructed"
1 Samuel 12:21: "And turn ye not aside: for then should ye go after  vain things, which cannot profit"
1 Samuel 12:21: "nor deliver; for they  are vain."
Job 6:18: "of their way are turned aside; they go  to nothing, and perish."
Job 12:24: "of the people of the earth, and causeth them to wander  in a wilderness where there is no way."
Job 26:7: "He stretcheth out the north over  the empty place, and hangeth the earth upon nothing."
Psalms 107:40: "upon princes, and causeth them to wander  in the wilderness, where there is no way."
Isaiah 24:10: "The city  of confusion is broken down: every house is shut up, that no man may come in."
Isaiah 29:21: "for him that reproveth in the gate, and turn aside the just  for a thing of naught."
Isaiah 34:11: "in it: and he shall stretch out upon it the line  of confusion, and the stones of emptiness."
Isaiah 40:17: "him are as nothing; and they are counted to him less than nothing,  and vanity."
Isaiah 40:23: "he maketh the judges of the earth  as vanity."
Isaiah 41:29: "are nothing: their molten images are wind  and confusion."
Isaiah 44:9: "They that make a graven image are all  of them vanity; and their delectable things shall not profit; and they"
Isaiah 45:18: "hath established it, he created it not  in vain, he formed it to be inhabited: I am the LORD;"
Isaiah 45:19: "unto the seed of Jacob, Seek  ye me in vain: I the LORD speak righteousness,"
Isaiah 49:4: "in vain, I have spent my strength  for naught, and in vain: yet surely my judgment is with"
Isaiah 59:4: "for truth: they trust in  vanity, and speak lies; they conceive mischief,"
Jeremiah 4:23: "the earth, and, lo,  it was without form, and void; and the heavens, and they had no light."