  We present wide-field, deep $K$-band photometry of 98 luminous early-type
galaxies (ETGs) from the MASSIVE survey based on observations taken with the
WIRCam instrument on the Canada-France-Hawaii Telescope. Using these images, we
extract accurate total $K$-band luminosities ($L_K$) and half-light radii
($R_e$) for this sample of galaxies. We use these new values to explore the
size-luminosity and Faber-Jackson relations for massive ETGs. Within this
volume-limited sample, we find clear evidence for curvature in both relations,
indicating that the most luminous galaxies tend to have larger sizes and
smaller velocity dispersions than expected from a simple power-law fit to less
luminous galaxies. Our measured relations are qualitatively consistent with the
most massive elliptical galaxies forming largely through dissipationless
mergers. When the sample is separated into fast and slow rotators, we find the
slow rotators to exhibit similar changes in slope with increasing $L_K$,
suggesting that low-mass and high-mass slow rotators have different formation
histories. The curvatures in the $R_e-L_K$ and $\sigma-L_K$ relations cancel,
leading to a relation between dynamical mass and luminosity that is well
described by a single power-law: $R_e\sigma^2 \propto {L_K}^b$ with $b \approx
1.2$. This is consistent with the tilt of the fundamental plane observed in
lower mass elliptical galaxies.
