God only knows! I think that they are an old military Q coding system. I don't think that the letters have any particular meaning.
Your definitions are not quite right though.
QFE - Presseure measured at the station
QNH - QFE mathmatically reduced/increased to sea level using ISA std figures
QFF - QFE mathmatically reduced/increased to sea level using actual conditions (temperature)
QNE - Emergency pressure setting used for low pressure/high altitude operations. I.E. when the actual pressure setting is off the scale of the altimeter.
Hope this helps,
Barnaby