Learner's definition of RELATED
1 : connected in some way 2 not used before a noun : in the same family
I just found out that my best friend and I are related through distant cousins.
We all call her “auntie,” but we're not actually related. [=we're not in the same family]
My stepmother and I are not related by blood. [=my stepmother and I do not share biological ancestors; our biological families are different]
My sister-in-law and I are related by marriage. [=my sister-in-law is married to someone in my family]
3 : belonging to the same group because of shared characteristics, qualities, etc.
Horses and donkeys are related.
closely/distantly related species
The words “play” and “playful” are related.