How do I explain to my 6 year old....uhhh?

Well, my 6 year old, Kris, got home from Kindergarten about 20 minutes ago & went into my 16 year old, Quinton's, room. He was in there getting ready for homecoming (Yay!), And my 6 year old came running out of his room saying, "QUINTON HAS A BIG !". i told him not to say that word anymore but now hes going around saying that. My 13 year old and 10 year old and husband are laughing and I'm trying to put our 1 year old down for a nap. The house is chaotic & if i could just get Kris to stop saying it, that'd be great!! I dont even think he really knos what the word means so im probly gonna have to explain it to him. Help please!?!