Strong's #4285: machshak (pronounced makh-shawk')
 from 2821; darkness; concretely, a dark place:--dark(-ness, place).
Brown-Driver-Briggs Hebrew Lexicon:
 ׁ 
  machshâk 
 
 1) dark place, darkness, secrecy
 
 1a) hiding-place
 1b) dark region
 1c) grave
 
  Part of Speech: noun masculine
Relation: from H2821
Usage:
This word is used 7 times:
Psalms 74:20: "Have respect unto the covenant: for  the dark places of the earth are full of the habitations of cruelty."
Psalms 88:6: "Thou hast laid me in the lowest pit,  in darkness, in the deeps."
Psalms 88:18: "hast thou put far from me, and mine acquaintance  into darkness."
Psalms 143:3: "my life down to the ground; he hath made me to dwell  in darkness, as those that have been long dead."
Isaiah 29:15: "from the LORD, and their works are  in the dark, and they say, Who seeth"
Isaiah 42:16: "that they have not known: I will make  darkness light before them, and crooked things straight."
Lamentations 3:6: "He hath set  me in dark places, as they that be dead of old."