"Blood sister" is a phrase commonly used to refer to a female sibling who shares the same biological parents as oneself. However, there are numerous synonyms for this phrase that can be used to describe the same relationship. Some of these include sister, sibling, sister by birth, genuine sister, biological sister, natural-born sister, or full sister. Additionally, other relatives that share a similar relationship with oneself could also be used as synonyms for "blood sister", such as half-sister, stepsister, or foster sister. In any case, the choice of synonym depends on the particular context in which it is being used, and the speaker's intention in describing the relationship.