an act of responding
a reply or reaction
something constituting a reply or reaction, e.g.:
something sung or said by the congregation or choir in reply to the priest or minister in a religious service
a change in the activity of an organism or any of its parts resulting from stimulation
the ratio of the power produced by an electrical system or device to the input
[Middle English respounse via early French respons from Latin responsum reply, neuter past part. of respondēre: see respond1]