  We observe and analyze tunable relaxation of a pure spin current by an
antiferromagnet in spin-valves. This is achieved by carefully controlling the
angle between a resonantly excited ferromagnetic layer pumping the spin current
and the N\'eel vector of the antiferromagnetic layer. The effect is observed as
an angle-dependent spin-pumping contribution to the ferromagnetic resonance
linewidth. An interplay between spin-mixing conductance and, often disregarded,
longitudinal spin conductance is found to underlie our observations, which is
in agreement with a recent prediction for related ferromagnetic spin valves.

Mesoscale and Nanoscale Physics