  We present new V-band differential brightness measurements as well as new
radial-velocity measurements of the detached, circular, 0.84-day period,
double-lined eclipsing binary system CV Boo. These data along with other
observations from the literature are combined to derive improved absolute
dimensions of the stars for the purpose of testing various aspects of
theoretical modeling. Despite complications from intrinsic variability we
detect in the system, and despite the rapid rotation of the components, we are
able to determine the absolute masses and radii to better than 1.3% and 2%,
respectively. We obtain M(A) = 1.032 +/- 0.013 M(Sun) and R(B) = 1.262 +/-
0.023 R(Sun) for the hotter, larger, and more massive primary (star A), and
M(B) = 0.968 +/- 0.012 M(Sun) and R(B) = 1.173 +/- 0.023 R(Sun) for the
secondary. The estimated effective temperatures are 5760 +/- 150 K and 5670 +/-
150 K. The intrinsic variability with a period about 1% shorter than the
orbital period is interpreted as being due to modulation by spots on one or
both components. This implies that the spotted star(s) must be rotating faster
than the synchronous rate, which disagrees with predictions from current tidal
evolution models according to which both stars should be synchronized. We also
find that the radius of the secondary is larger than expected from stellar
evolution calculations by about 10%, a discrepancy also seen in other (mostly
lower-mass and active) eclipsing binaries. We estimate the age of the system to
be approximately 9 Gyr. Both components are near the end of their main-sequence
phase, and the primary may have started the shell hydrogen-burning stage.
