I provided the definition to show that 'tribes' is not necessarily the definition of 'ethnos.' Yes it could be, but it is not at all a 'preferred' definition.
The reason I say it is preferred is that it agrees with scripture [Matthew 10:5-6][Matthew 15:24][John 21:15-17][Galatians 2:7][James 1:1][1 Peter 1:12]
That should read 1 Peter 1:1-2 not 1:12