Nothing came immediately to mind with the letter E when preparing for this challenge. So I googled inspiration! Amongst the thousands of genealogy-related "e" words, a little gem popped up on the unusually titled website The Phronistery and its Compendium of Lost Words.
As the title suggests, the words have been lost from English, probably because no one could pronounce them! Amongst tongue-twisteres like though, was the easy to articulate "exlineal".
E, therefore, is for Exlineal. As in 'out of the direct line of descent'. 
Although no longer a word (and apparently only in use in 1716!) I reckon genealogists should look at bringing exlineal back into usage. It sure beats 'cousin three times removed'! It's also a helpful way to describe what it is I am doing with our family tree. At the moment I am following the direct line of ascent from my maternal grandfather, or the paternal lineal path from Pa.
Let me demonstrate with pictures:
For our purposes, Pa (1) is a lineal descendant of Alexander Cameron as is Alexander Cameron (2) and Jessy Horn (3). Pa is also a lineal descendant of Robert Cameron but Alexander (2) and Jessy (3) are exlineal descendants of Robert ie, they are not part of the direct line.
But don't think for a minute that they are any less important to the tree. It's important to follow the exlineal branches cos you'll never know where they might lead you and who you might find... As another genealogist said:
"Treat the brothers and sisters of your ancestors as equals … even if some of them were in jail." 
So, who's for bringing back 'exlineal'?
 Definition from The Phronistery: Compendium of Lost Words