I've read some corny ass definitions of the word "trill," but some words and phrases in black vernacular don't require such explanations. Those who it was meant for, get it. We get it through cultural comprehension. Solange said it best, "some shit is for us."
Bun B of UGK explains the origin of the word 'trill' in a commentary BET commentary clip.
He explains that "trill" is a word that started in the Texas prison term. "there's no clothing you can put on that'll make you trill, you can put on a hat that says trill, but it wont make you trill"
"Being trill means being 101% about yourself and when you dealing with people, it's about not compromising yourself"