Half Note

The length of time it takes for a piccolo to stay in tune.

James: "Hey, I think that piccolo player stayed in tune for a whole note!"
Alex: "No, silly, everyone knows piccolo players can only stay in tune for a half note."

Half open pocket knife

Half a bar. Or a semi erect penis

“Man that chick was hot. I’ve got a half open pocket knife in my pants.”

half-first great-cousin-aunt

Grandparent’s female half-first cousin.

My half-first great-cousin-aunt is a good person.

half-first cousin-nephew

Half-first cousin's son.

My half-first cousin-nephew is a good boy.

half Spock

Fingering your girlfriend in both holes, using the index and middle finger. A full Spock would be using your index and middle fingers in one hole, and the ring and little finger in the other.

My lady wasn't satisfied with only a half Spock, so I had to add more fingers.

half-great-uncle

Grandparent's half-brother.

My half-great-uncle is a good person.

half-great-uncle

Grandparent's half-brother.

half-great-uncle.