Question: A technical writer wants to change a label of a table column. He says it is not clear. I, a usability expert, am against it. Who should have the last word?

Answer: 
Per Chad's comment, the product owner is the arbiter of such decisions. It is up to you and the technical writer to make your case for the change; vice versa it is up to the product owner to gather the evidence from you two and any other sources.
Test It.

Go and wander around the shops at lunchtime (ie do **not** ask people in your company - who will be too close to the jargon) and ask random people what the two alternate label words mean to them.