I have seen claims that it stood for both "Cruiser Voler" and "Carrier, aViation" (with CA already standing for Cruiser, Armored). What do we know about the abbreviation "CV"? Do we know of any military or naval documents that shed light on this?
This nomenclature dates to 1920, and was specified in General Order No. 541, "Standard Nomenclature for Naval Vessels": https://www.history.navy.mil/research/library/online-reading-room/title-list-alphabetically/g/general-orders/general-order-no-541-1920-standard-nomemclature-naval-vessels.html
The easy part is C = cruiser. What about V? V means "heavier than air" aircraft. We have the pair of abbreviations:
V - heavier-than-air
Z - lighter-than-air
(Today, we have V = "fixed wing" and H = "helicopter", but the above were sufficient for 1920.)
The order doesn't say whether the V is derived from any particular word; no explanation was given, so the common suggestions of Voler, aViation, and heaVier-than-air are just guesses. Similarly, the suggestion that Z comes from Zeppelin is also a guess (Goodyear Zeppelin, a joint project between Goodyear and Luftschiffbau Zeppelin, built airships for the Navy, but was only formed in 1923, so Z for Zeppelin would come directly from the German, if this is the origin of Z). Z and V were the two letters at the end of the alphabet not already used, and there might be no more to it than this.