How do you name a beast that was named before taming?

[Nenuarë]

Usually I give them a new name.

Loque'nahak is now Brumorage
Samba is now Hamarkhis
Skoll is now Dùnraz
Karoma is now Brumétoile
The Razza is now Szörny
Ashtail is now Refurinn

The only exception is Gezzarak, the purple warp stalker. I coudn't find another name for her, Gezzarak fits her perfectly

I forgot Arcturis, now call him Givrecroc (just tamed tonight )

[Cialbi]

If it's an RP reason you feel you should keep the name, consider (i) the pet isn't sentient and doesn't call itself anything, so whatever name it's given must just be what some local who saw it called it and your name for it is just as perfectly valid, and (ii) your toon, stumbling upon this beast in the wild, probably wouldn't even know the name someone else gave it, as it's not like they'd actually have their name floating above their head

Wain, you're a petty thief - you keep stealing what I was about to say! Since we tame the beasts as wild animals, we can pick any name we want and teach our new pet to respond to said name. If the beast had a name before being tamed, it's quite likely that the name had no significance to the beast.