NDP Leader Thomas Mulcair says terrorism is not the right word to describe last week's attack on Parliament Hill.

Members of Parliament gathered for their weekly caucus meetings Wednesday morning exactly one week from the time a man with a rifle stormed Parliament's Centre Block after killing Corporal Nathan Cirillo who was standing guard at the National War Memorial.

"Frankly the information that is now available to the public comforts me in my choice not to use the word terrorism in describing the act that took place here," Mr. Mulcair told reporters following Wednesday's meeting.

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"It doesn't take away from the horror of what took place. It doesn't make it any less criminal but I think there's a distinction to be used and when you look at the background of the individual and what was actually going on that the use of that word was not the appropriate one. That's our point of view. That's my point of view."

Prime Minister Stephen Harper had described the attack as an act of terrorism during his televised address to the nation last Wednesday evening.

Mr. Harper took issue with Mr. Mulcair's comments Wednesday afternoon during Question Period.

"There's no contradiction to individuals who may have a series of personal, financial and mental difficulties and also Mr. Speaker, be engaged in terrorist, jihadist activities as indeed Mr. Speaker the police have already said," said Mr. Harper. "We don't think it helps the Canadians to do anything but address these matters head on and face them for what they are."

Liberal Leader Justin Trudeau said he bases his use of the word on the opinion of the RCMP.

"The RCMP was clear, these were acts of terrorism. These were acts of terrorism," Mr. Trudeau said Wednesday.

The Criminal Code of Canada contains a detailed definition of "terrorist activity" that is more than 800 words long.