You're So Old....

...that no one even knows what you mean!
I have to admit, one of my biggest pet-peeves on baby-name websites is oversimplification. While the etymologies of many names are fairly concrete & easily traced, others have become lost or muddled over the millennia.

• Aaron--the form of Aaron hasn't changed much--it's Aharon in Hebrew. But, unlike most Biblical names, it's only given to one person in the entire Bible! With no other contexts, or evolution of form, it's hard to determine its source. While it's possibly Hebrew, "mountain" or "brightness, light"; it's more likely an Egyptian import. 
• Anthony--Although this is sometimes listed as meaning "flower", that's not quite true. The name has been around for a couple thousand years or so, but it didn't start being spelled & pronounced with "th" until a few hundred years ago, when someone decided it would be better if it looked like anthos, the Greek word for flower. Its actual origin was most likely Etruscan.
• Camilla--the original Latin (masculine) form is Camillus, which also happens to be a word in Latin--"acolyte". Experts agree it's probably coincidental, and that the name was imported, probably from Etruscan. 
• Carson--it was a surname first...that about all that's certain! It could be related to the Scottish name/surname Kerr, but is more likely from a French location, like Coursan or Carsan.
• Cormac--'Mac' is Gaelic for "son of"; it's the 'Cor-' that causes problems. Possibilities include "raven" [fig. "myth, legend"], "corruption", "charioteer", or simply "Corb" [a Titan-like figure in Irish myth].
• Eleanor--it's often listed as a variant of Helen, but is more likely from a Germanic name. One popular theory is that it comes from the Provençal phrase alia Aenor--Aenor being the mother of the first prominent Eleanor, Eleanor (Alíenor) of Aquitaine. However, records indicate she may not have been the first Eleanor/Alíenor, in which case, her name was likely a clever play on words.
• Katherine--originally Aikaterine in Greek, it was changed to resemble katharos, "pure". Aikaterine has several possible sources: the Greek personification of skillful hands, Hekateros; the Greek goddess of magic and night, Hecate; or it could have even been imported into Greek from another culture, like Egyptian.
• Mary--This is the form we got after the Hebrew Miryam passed through Greek, and then Latin. There have literally been whole papers written on the myriad of possible sources. The most likely Hebrew derivations include "sea of myrrh" [fig. "bitter" or "strong"], "lady of the sea", "shining sea, star of the sea", "drop of the sea", "rebellion", "beautiful one". It could also have been originally Egyptian, "beloved".
• Monica--It's possible that the name is related to Latin "advisor" or Greek "one", but since the Monica who brought the name to the Christian world was African (St. Monica, St. Augustine's mother), it's almost certainly of Punic or Numidian origin.
• Reilly--The English form (usually spelled Riley) is pretty easy to parse: "rye field". The Irish form, however, was shortened/Anglicized from something like Raghallach, which is not so easy to parse. It  could be from Old Norse, or it could be a relative of Kelly/Ceallach, which doesn't have a certain derivation either! Possibilities include "bright-headed", "church", "valiant", or "sociable".
• Sabrina--The Latinized name of the Welsh Hafren river (Severn in English), no one seems to have any clue where it came from! Folklore links the river's name to a drowned girl or a nymph, but it's more likely the place-name came first. 
• Teresa--originally Therasia in Greek, it has a few different possibilities: "summer", "to hunt", "harvest", or from the island of Therasia, which was possibly named for an ancient ruler, Theras, his name likely derived from 'ther', "wild creature".
• Thelma--Never really popular, this one's nevertheless been popping up in records for centuries. It's possible that it's from Greek thelema, "will", but is more likely a shortened form of a Germanic name.