differential
differential-pressure
differentiate
differentiator
differently-skilled
difficult-to-break
difficult-to-cut
difficult-to-drill
difficult-to-extrude
difficult-to-form
  difficult-to-machine
difficult-to-make
difficult-to-mill
difficult-to-pump
difficult-to-quantify
diffraction
diffractometer
diffuse
diffused
diffuser
diffusion