Jaslyn

Well some say it could come from Jocelyn. Which I can see. It could be a variant. But based on the pronunciation it makes more sense if it is Jasmine plus Lynn. It is pronounced (jazz-lynn), Jas in Jasmine is also pronounced Jazz. So I believe it to be this.

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It is probably the English version of FLOWERY LAKE. Jasmine the flower and Lynn means lake. Add the two contents together and you flowery lake. Does that make sense? I am just thinking out loud haha lol!

Another site had this to say about the name Jaslyn and Jazlyn:
English Modern variant of Jasmine; combination of Jocelyn and the musical term 'jazz'.

Jaslyn - a modern day variant of Jocelyn. Jocelyn was a male name in medieval times then later adopted as a female name. Jaslyn is English and means Joy.

I believe this name could possibly be related to the name Jocelyn. I may be wrong, but they do seem a bit similar in spelling and pronunciation. Just a thought.