Omni-Achillian is a label under the Omnisexual umbrella. It is mixing two different labels (Omni and Achillian), while also not using harmful labels such as Omni-Vincian. It is when a man, or male-aligned nonbinary person may be attracted to all genders, but they prioritize their attraction to men and/or male-aligned people. This does not mean that the user of the term is Vincian/Toric, this just means that the user of the term has a preference to men.
History
The term Omni-Achillian can be traced to the Tumblr user “kokichisleftasscheek”, on October 22, 2020.
Flag
The flag meaning is as such, starting from the bottom:
Light Teal - Attraction to male-aligned nonbinary people.
Light Blue - Being male-aligned.
Blue - Being a man.
Deep Blue - Attraction to men.
Black - Attraction to nonbinary people.
Deep Pink - Attraction to women.
Light Pink/Purple - Attraction to women/women-aligned people
Etymology
The term Omni-Achillian comes from the Latin prefix “Omnus-“, meaning “all”, and the word Achillian, which is commonly used to refer to men who love men (or mlm for short.)
Resources
https://kokichisleftasscheek.tumblr.com/post/632718817947172864/omni-sapphic-omni-achillian