Arguing about semantics with kids

Last night at the kids' bedtime I found myself in a screaming match with my nine-year-old, who was trying to enforce an instruction to my five-year-old to get into her bed. Without asking if I wanted her help, the nine-year-old pushed the five-year-old, causing her to bump her head. This caused the five-year-old to cry and me to accuse the nine-year-old of performing unasked-for enforcement. The nine-year-old responded by denying that she was enforcing. She thinks that she can call it by a different name she are not actually committing the crime! My 14-year-old was a master at this type of name-changing. Does anyone else out there struggle with their kids changing the term defining what they are doing in order to avoid being called on their behavior?

-- Hoarse parent in Minneapolis