This is a very unusual name, I've never heard it in my life, despite being Greek. However, this is feminine, the ending is female, therefore probably it was wrongly stated as masculine. If there was a male version, that should be Nomikos (Νομικός). [noted -ed]
I really like this name --- for a girl. I usually don't like making boy names into girl names, but Nomiki has a feminine quality that cannot be ignored. It's quite pretty.
As a Dutch couple living on Kos, we first heard of the name Nomiki from friends on Kalymnos, where the name is said to have originated. Since we liked the name very much, we chose it for our daughter, who is now eight years and, to our knowledge, the only Nomiki in Holland. We call her Nomi when she is girlish, and Mik when she is tough.
The meaning is correctly given as Greek for "related to the law" or "legal". We understand the name is not very common even in Greece, except for the - tiny - island of Kalymnos, where the name may have originated.