  We derive stellar parameters and abundances (`stellar labels') of 40,034
late-B and A-type main-sequence stars extracted from the Large Sky Area
Multi-Object Fiber Spectroscopic Telescope Medium Resolution Survey
(LAMOST--MRS). The primary selection of our early-type sample was obtained from
LAMOST Data Release 7 based on spectral line indices. We employed the Stellar
LAbel Machine (SLAM) to derive their spectroscopic stellar parameters, drawing
on Kurucz spectral synthesis models with 6000 K $< T_\mathrm{eff} <$ 15,000 K
and $-1$ dex $< \mathrm{[M/H]} <$ 1 dex. For a signal-to-noise ratio of $\sim
60$, the cross-validated scatter is $\sim$75 K, 0.06 dex, 0.05 dex, and $\sim
3.5\,\mathrm{km\,s^{-1}}$ for $T_\mathrm{eff}$, $\log g$, [M/H], and $v\sin i$,
respectively. A comparison with objects with prior, known stellar labels shows
great consistency for all stellar parameters, except for $\log g$. Although
this is an intrinsic caveat that comes from the MRS's narrow wavelength
coverage, it only has a minor effect on estimates of the stellar rotation rates
because of the decent spectral resolution and the profile-fitting method
employed. The masses and ages of our early-type sample stars were inferred from
non-rotating stellar evolution models. This paves the way for reviewing the
properties of stellar rotation distributions as a function of stellar mass and
age.
