Why is any object we don't understand always called a thing?

Related:

• This child is about to wipe out every living thing on Earth.
  Now what do you suggest we do? Spank it? -- McCoy...
• I bet they've redesigned the whole sickbay too. I know engineers -
  they just *love* to change things! -- McCoy, "The...
• An object in motion will always be headed in the wrong direction.
  David...
• Kerla: "In any case, we know where this is leading.
  The annihilation of our culture." McCoy: "That's...
• Scott: "How do we know he didn't invent the thing?" McCoy:
  "Yeah." -- "STIV:TVH", Stardate 8390...
• McCoy: "Dear Lord, do you think we're intelligent enough to.
  Suppose, what if this thing were used where life...
• Kirk: "Some people are afraid...of what might happen.
  I was terrified." McCoy: "What terrified you, specifically...
• And if I laugh at any mortal thing, 'T is that I may not weep.
  Lord Byron (1788-1824) -- Don Juan, Canto iv, Stanza...
• Soon to be a major motion
  picture...