What do u think shadow and bone means

I have actually wondered this as well for quite sometime now. What I think (and this could be completely wrong) is that the shadow portion of the title is a metaphor for The Darkling or a metaphor for her own inner darkness or her own inner shadows within. Then the bone portion can stand for her amplifier, the stag’s antlers (because antlers are made of bone I’m pretty sure). So that is my outlook on the title. Her inner darkness/The Darkling and her amplifier helps to pretty much kick off the rest of the trilogy and we see in all three of the books her struggle with her shadow (The Darkling or her own inner darkness) and bone (her amplifiers).