I'm translating part of Pliny's letter about the death of Fundanus' daughter, and there's this one word that I've never seen before, nor can I find it anywhere: amabilius. It's making it tricky to get the syntax of the whole sentence, so if anyone knows what this word is...it's meaning, or anything else about it, I'd be extremely grateful. I'll give the surrounding text in case it helps, but don't worry, I've got the meanings for the rest of the words already

"Qua puella nihil umquam festivius amabilius, nec modo longiore vita sed prope immortalitate dignius vidi."
I'm pretty sure that it starts out with "The cheerfulness of that girl" or something to that effect, but I'm not sure about the placement of 'nihil' and 'numquam' since I'm not sure what this 'amabilius' is.
Thanks in advance for any help!