non-blood relations

half-brother

ˈhalf-ˌbrother BrE AmE noun [countable]
a brother who is the son of only one of your parents ⇨ half-sister

half-sister

ˈhalf-ˌsister BrE AmE noun [countable]
a sister who is the daughter of only one of your parents ⇨ half-brother

stepdaughter

step‧daugh‧ter /ˈstepdɔːtə $ -dɒːtər/ BrE AmE noun [countable]
a daughter that your husband or wife has from a relationship before your marriage

stepson

step‧son /ˈstepsʌn/ BrE AmE noun [countable]
a son that your husband or wife has from a relationship before your marriage
 

stepsister

step‧sis‧ter /ˈstepsɪstə $ -ər/ BrE AmE noun [countable]
the daughter of your stepmother or stepfather

stepbrother

step‧broth‧er /ˈstepbrʌðə $ -ər/ BrE AmE noun [countable]
the son of your stepmother or stepfather

stepmother

step‧moth‧er /ˈstepmʌðə $ -ər/ BrE AmE noun [countable]
a woman who is married to your father but who is not your mother
• • •
THESAURUS
▪ mother a female parent: My mother and father are both teachers.
▪ mum British English informal, mom American English informal used when talking to your father, or about someone's father: My mum and dad won’t mind if you want to stay the night. | Mom, where’s my sweater?
▪ mummy British English, mommy American English a name for mother, which is used especially by young children or when you are talking to young children: Where’s Mummy, Abbie?
▪ ma American English old-fashioned used when talking to your mother, or about someone's mother: Ma stirred the soup on the stove.
▪ mama old-fashioned used when talking to your mother, or about someone's mother: Mama seldom disagreed with Papa.
▪ stepmother (also stepmum British English informal, stepmom American English informal) a woman who is married to your father, who is not your mother but often acts as your parent: the wicked stepmother in fairy stories

stepfather

step‧fa‧ther /ˈstepfɑːðə $ -ər/ BrE AmE noun [countable]
a man who is married to your mother but who is not your father
• • •
THESAURUS
▪ father a male parent: My father’s a doctor. | He’s a father of three.
▪ dad informal used when talking to your father, or about someone's father: Can I borrow your car, Dad? | Her dad retired ten years ago. | My dad was in the army.
▪ daddy a name for father, which is used especially by young children or when you are talking to young children: Where’s your daddy? | Daddy, can I have a drink, please?
▪ pop American English informal (also pa old-fashioned) used when talking to your father, or about someone's father: I helped Pop fix the gate this morning. | Can I help, Pa? | He is in New York with his Pop's credit card, eating all the ice cream and pizza the city has to offer.
▪ papa old-fashioned informal used when talking to your father, or about someone's father: Papa had forbidden me to go. | She saw her papa 's face change at this news.
▪ sb’s old man informal someone's father – used when talking about him in a way that is not very respectful: His old man wouldn’t let him use the car.
▪ stepfather (also stepdad informal) a man who is married to your mother, who is not your father but often acts as your parent: Her stepfather is really nice.

sister-in-law

ˈsister-in-ˌlaw BrE AmE noun (plural sisters-in-law) [countable]
1. the sister of your husband or wife
2. your brother’s wife
3. the wife of the brother of your husband or wife

brother-in-law

ˈbrother-in-law BrE AmE noun (plural brothers-in-law) [countable]
1. the brother of your husband or wife
2. the husband of your sister
3. the husband of your husband or wife’s sister
⇨ sister-in-law