The acronym SIB stands for siblings, which are brothers and sisters related by blood. The crossword solutions for SIB are SIS (3 letters), BRO (3 letters), SISTER (6 letters), REL (3 letters), and CLAN (4 letters). SIS and BRO are abbreviations for SISTER and brother, respectively. SISTER is the full word for SISTER, while REL is a shortened form of relative, which is a broader term for family members related by blood. Finally, CLAN is a term used to refer to a group of people related by blood or marriage.