First meaning is gory and bloody and horrible!  Then on the word moved to “sad”, then melancholy and dull.  “Drear” is a poetic shortening.

• 02.028 Not far ahead were dreary hills,
• 03.001 and drear it looked,
• 09.012 This is the dreariest
• 10.003 Dreary as had been his imprisonment
• 14.002 and drear even
• 19.004 So sad and so dreary?

“dreary, adj.” OED Online. Oxford University Press, June 2015. Web. 27 July 2015.