four-horn
Fourier
Fourier-transform
four-layer
four-level
four-of-eight
four-out-of-eight
four-output
four-over-four
four-phase
  four-point
four-pole
four-port
four-region
four-speed
four-stacked
four-terminal
four-track
four-way
four-wire
Fowler-Nordheim