Yup - piano actually means 'soft' - forte, on the other hand, means 'strong' - often meaning to play loud in music. The name piano for the musical instrument is a shortened name - the complete name of the instrument is 'Piano/Forte' - meaning an instrument that can be played 'Soft' or 'Loud'.
* Imagine the original keyboard was a harpsichord. It is a harp with a mechanism that plucks the string, this was originally the stem from a feather. As you push the key down it would pluck the string, and there was only one volume to it - pushing the key faster or slower made no difference in the volume.
* The piano (or Piano/Forte) produces sound by a hammer hitting the string; as you push the key down the hammer hits the string. If you press harder or faster the hammer hits harder creating a louder sound - softer press, softer sound.
So the true meaning is 'soft' as it applies to hitting - if you are in a fight don't be swinging 'piano' punches.