Took my DCs to a music group this morning. DS dad usually takes DS but FIL died so I took him along with DD. Music lady said ah this is your half sister, what's your half sister called etc. DS
DS knows they have different dads but has never heard the term half before. On the third time she said it, I firmly said "its sister, we use the term sister".
AIBU to find the term half sister uncomfortable? As far as I'm concerned they are brother and sister, end of.