Oddly enough we were discussing Q codes at work the other evening. Not sure where the Q came from but others have posted probable sources.
Thoughts on a few of them and yes, I have a book but Lord knows where it is.
QFE Field Elevation
QNH Newlyn High (High water mark in Cornish port?)
QDM Direction Magnetic
QDR Direction Reciprocal
QTE True ??????
QGH Ground Homing
QSY See You!