A childs parent is both their sister and their mother.
This word derives from the combination of two words sister and mother. The words used is the short form of each words which is sis and mom. The second meaning of sister which is a female offspring having only one parent in common with another offspring. Mom which means 1. A female parent.
"In incest families common found in the southern states of North America sisters of brothers are also found to be their mothers."
"Bobby Joe who is Billy Bob's sisom recieves notice to attend the parent teacher conference on parent teacher night."