probably from English dialect geek, geck fool, from Low German geck, from Middle Low German
1 : a carnival performer often billed as a wild man whose act usually includes biting the head off a live chicken or snake
This is Crystal Lil from the novel Geek Love (my senior thesis) in the process of her Geek act.
In the early days of Al's circus, when Al Binewski was still a young lad and Crystal Lil was a mere slip of a lass, a series of events led to their love and future marriage.
The normal circus geek, a young Yale-boy, decides to go back to school and get his education. Alas, Al is now one geek short of a show. Lil, a girl born into nobility who ran away to the circus, sees Al's plight. In her love and adoration, she offers to be the new geek. Al is concerned. No one had ever heard of a female geek before and he was afraid she may get hurt. However, in his desperation he reluctantly agrees.
Lil became a hit. People came from far and wide to see the geek femme fatal. She danced and sang German folk songs as the blood from the decapitated chickens splattered on her white rags.
Al became enamored with the enigmatic woman and they later married. Eventually Lil became Crystal Lil in her short stint as a trapeze artist. Her career was ended when she took a crippling fall. Despite Lil's ended career Al and Lil's love would sustain and be essential to when the circus starts to fail.
Though that's a story for another day.