I find little etymological notes like this interesting. This brief post gives the background behind Sir Galahad’s name.
If you read older sources, the older name for Galahad is “Galaad.” That’s the Latin Vulgate spelling of “Gilead.” Sometimes you see people adding an extra H for their pronunciation convenience, and that probably would be where the H in Galahad came from.
Of course, Gilead probably came in as a Latin/English/Frenchification of his original name, Gwalchavad, which is super-Welsh and would be way too hard to say if you weren’t from Wales or Brittany. Defaulting to a nice Biblical name would have been a good compromise. It may have led to Galahad becoming more saintly of character, too.
Anyway, I’ve known this for a while, but it’s not something obvious or well-known, so I thought I’d throw it up there for the Internet’s sake.