The original connotation was used in the following: "word is bond" meaning literally "I speak the truth, my word is my bond."
"Word to your mother" is an extended affirmation of the truth denoting confidence in the veracity of one's statement.
"Word up" means nothing at all. Unless you enjoyed that ridiculous song by Cameo from the 80's sung by that guy who sounded as if he'd had his adenoids removed.
Yo, pretty ladies around the world
Got a weird thing to show you so tell all the boys and girls
Tell your brother, your sister and your mama too
'Cause we're about to throw down and you know just what to do
Libra
- throw your hands in the air like you don't care