Excuse

logic that leads to doing less work that you know you should be doing for superior moral reasons anyway

Example:
"I dont want to work today because I have neckpain"

Ok, you should probably still do it and fix your neckpain later as best as you can.

What is not a valid excuse? This is where the 'moral' bit comes into play.
Technically the old definition would call this an excuse too:
"I dont want to kill those 15 starving children because I dont like killing".

But a real excuse in my humble opinion is an excuse only when you duck out of doing something that would be the *right* thing to do - something you should be doing for a higher purpose.