VANCOUVER — What's another word for unreasonable?

A Federal Court judge has ruled a British Columbia prison was wrong to deny an inmate's request to buy a thesaurus, rejecting the Mountain Institution's argument that the reference book is not educational.

In a playful ruling that quotes "Alice in Wonderland" and points out a thesaurus is not a fire hazard, Judge Sean Harrington orders Correctional Service Canada's grievance board to reconsider inmate Ken MacKay's request to buy a $20 book to improve his language skills.

"Why was the thesaurus not considered an educational textbook? Without doubt it is educational," writes Harrington in a written decision posted to the court's website this week.

"In my opinion, the decision was unreasonable."

MacKay, who is serving a life sentence at the prison in Agassiz, east of Vancouver, submitted a request to purchase an Oxford paperback thesaurus worth $23.14. The judgment doesn't indicate what crime MacKay is serving time for, but notes he is in the sex-offender maintenance program.

But the prison's wardens denied the book request, saying the purchase would put MacKay over the maximum of $1,500 of personal property inmates are allowed to keep in their cells.

Educational textbooks and supplies are exempt from that limit, but prison wardens -- and three levels of appeal within the federal corrections system -- said MacKay didn't require a thesaurus for his participation in the sex-offender program and therefore the book should be considered a personal item.

The prison said MacKay should instead borrow one from the prison's library.

According to the judgment, MacKay insisted he needed the thesaurus to improve his English and help him with writing assignments that are part of his program. He said he wanted his own copy so he could take notes in the book, which would be against the rules if he used one of the prison's copies.

He appealed the decision to Federal Court, where a lawyer for the federal attorney general argued the wardens acted in good faith and the decision was fair and within their discretion.

Harrington disagreed, suggesting the prison was trying to change the definition of what can be called a textbook.

The judge quoted a scene from Lewis Caroll's book "Alice's Adventures in Wonderland," in which Alice is talking to Humpty Dumpty about the meaning of words.

In the passage, the giant egg from the nursery rhyme tries to convince Alice that words can mean whatever he says they do.

"In this court, Humpty Dumpty falls," wrote Harrington.