recherchez un mot, comme fleek :
 
1.
Emphatically exhibits the sincerity of your seriousness. The classic use is to close a letter with it.
Dear Urban Dictionary:


Thank you in advance for considering “sinseriously” in your Urban Dictionary.

Were sinseriously to be included in The Urban Dictionary, that would make my day, perhaps even my week.

Sinseriously,
Cyprus Denton Fekks
de Cyprus Denton Fekks 19 février 2010
 
2.
To be sincere and serious at the same time.
"Dude, sinseriously, im sorry"
de LilRayRay 24 juillet 2008
 
3.
"sinseriously" is a super fun loving word that can be used to sign a card with. It is a great way to let someone know how much you care about them and that you are serious and sincere about everything you wrote on a letter. It is a cherry on top.
Thanks for being my friend and i hope you enjoy your present

"Sinseriously", Joe
de valkayerie 9 juillet 2011