[net.puzzles] wordplay

set@bnl.UUCP (William Tatum) (08/23/84)

[a worded problem is always the best.]

here is a tough word problem.all the cluses are given to unveil the identity of the missing element:
      with thieves i consort
      with the vilest,in short
      i am quite at my ease in deprevity;
      yet all devines use me,
      and savants can't lose me,
      for i am the center of gravity.
       -->what am i?<--