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1.
To be going through withdrawals usually associated with drugs. More specifically marijuana.
Got any pot Pip? I'm jonsen.
by Dudeman January 10, 2004
 
2.
Jonsen pronounced (joan + sin) is to be boo loving or communicating with someone you like in a sweet way whether in person or on the phone... etc
Tisha need to stop jonsen on the phone with her boyfriend.
by Betty Boopi September 24, 2006