Someone who isn't jewish but acts jewish, has jewish friends, and considers themself jewish.
"Did you see Mordechai's girlfriend? Would his parents be ok with her not being jewish?" -guy #1
"She's jewishish so his parents say its ok as long as they don't get married." -guy #2
Part taking in Jewish religion where it doesn't belong such as a catholic church during a session. Very disruptive and distracting for and to the community.
"Was Kevin Jewishing again?"
"indeed he was Tom."
"Kevin needs to take thatelsewhere, it's affecting our praising of God"