A derogatory term to denounce soldiers with mental illness is still being used in the Australian Army, former soldiers have said.

The word "malinger", which means to pretend injury to get out of work, is used by soldiers to denigrate comrades struggling with depression.

"If people were depressed they certainly didn't talk about it," said one former soldier of the Royal Australian Regiment's 5th battalion (5RAR), who wants to remain anonymous.

"A lot of people choose not to [talk] because it can bring on derogatory terms like 'linger' which is short for malingerer, which basically means you're trying to get out of doing your work."

Mental health expert Professor Patrick McGorry said the term had been around for a long time in Australia.

"The term 'malingering' has a long history in the military, it goes back to the First World War and beforehand, where any kind of mental decompensation or problems were seen almost as a form of cowardice," he said.

The former Australian of the Year said the term put "tremendous judgement and stigma" on people who needed help.

"It can be very damaging because it stops people reaching out to their mates for help, that's what Australians pride themselves on, being able to rely on your mates to help you when you're in trouble," Professor McGorry said.

Calling people names is damaging and stops them seeking help, Professor McGorry says. ( Facebook: 5RAR )

Soldiers told to 'suck it up'

The former 5RAR soldier left the Army after completing his four-year initial service and says comrades were anxious about speaking up.

"They'd be afraid that they'd get punished or told you need to just 'suck it up, you're trying to get out of field', so people are pretty hesitant if they're feeling down to go and talk about it, " he said.

The ABC has contacted Defence seeking a response about the use of the word in the Army.

The former soldier said morale at 5RAR was "average to poor most of time" and there were at least three suicides during his time in Darwin.

"It was a good workplace but a lot of the times it was a lot shitter than it probably needed to be, just due to morale," he said.

Private Bryce Muscat from 5RAR's Bravo company was found dead inside his unit in Palmerston on May 4.

Mr Muscat's friend, who also wishes to remain anonymous, said the 23-year-old was upset about the treatment of a fellow comrade at 5RAR Bravo, who tried to self-harm last month.

"He had particular concerns about some within the unit or the company, he just felt that there may have been some incompetence," he said.

In the days following Private Muscat's death, soldiers from 5RAR travelled to Mount Bundey near Darwin for live-fire training. It was during that training on May 10 that Private Jason Challis was accidentally shot and killed.

Common for soldiers to be ridiculed

Another former soldier at 5RAR has told the ABC it was common for soldiers to be ridiculed if they were underperforming, especially during fitness tests.

Private Bryce Muscat, 23, took his own life in Darwin on May 4, 2017. ( Supplied )

"Just derogatory terms like piece of shit, you're a shit c***. Just a lot of derogatory stuff," he said.

"Things like (at) fitness assessments, people you could see were physically overweight, they underperformed in physical assessments and a lot of time that brought on a lot of shaming, name-calling, even from people from a higher rank."

In a statement responding to bullying claims within ranks, Defence said it encouraged its members to report any instance of unacceptable behaviour.

It said it reviewed all incidents of bullying and harassment between January 1, 2016, and May 16 this year, and said there were about 300 recorded incidents of unacceptable behaviour nationally.

In Darwin's 5RAR, there were three incidents of bullying and harassment, with one member separated from the Army, one member disciplined, and one incident still subject to an inquiry.