Calling slaves "immigrants" is a euphemism. There's a difference between those who chose to come here and those who were kidnapped and brought here. A vast difference.
No one is denying that. Still, per the definition, "immigrant" applies to slaves, indentured servants and prisoners as well as those who came to the US of their own free will.
Look at Australia's Botany Bay. Immigrants or not? They
were immigrants, albeit unwilling ones.
First Australian penal colony established - Jan 26, 1788 - HISTORY.com
JANUARY 26, 1788 : FIRST AUSTRALIAN PENAL COLONY ESTABLISHED
The first 736 convicts banished from England to Australia land in Botany Bay. Over the next 60 years, approximately 50,000 criminals were transported from Great Britain to the “land down under,” in one of the strangest episodes in criminal-justice history.
The accepted wisdom of the upper and ruling classes in 18th century England was that criminals were inherently defective. Thus, they could not be rehabilitated and simply required separation from the genetically pure and law-abiding citizens. Accordingly, lawbreakers had to be either killed or exiled, since prisons were too expensive. With the American victory in the Revolutionary War, transgressors could no longer be shipped off across the Atlantic, and the English looked for a colony in the other direction.
Captain Arthur Phillip, a tough but fair career naval officer, was charged with setting up the first penal colony in Australia. The convicts were chained beneath the deck during the entire hellish six-month voyage. The first voyage claimed the lives of nearly 10 percent of the prisoners, which remarkably proved to be a rather good rate. On later trips, up to a third of the unwilling passengers died on the way. These were not hardened criminals by any measure; only a small minority were transported for violent offenses. Among the first group was a 70-year-old woman who had stolen cheese to eat.
Although not confined behind bars, most convicts in Australia had an extremely tough life. The guards who volunteered for duty in Australia seemed to be driven by exceptional sadism. Even small violations of the rules could result in a punishment of 100 lashes by the cat o’nine tails. It was said that blood was usually drawn after five lashes and convicts ended up walking home in boots filled with their own blood–that is, if they were able to walk at all.
Convicts who attempted to escape were sent to tiny Norfolk Island, 600 miles east of Australia, where the conditions were even more inhumane. The only hope of escape from the horror of Norfolk Island was a “game” in which groups of three prisoners drew straws. The short straw was killed as painlessly as possible and a judge was then shipped in to put the other two on trial, one playing the role of killer, the other as witness.
The definition of the word"immigrant" does not specifically include slave or, more precisely, the transport of African slaves to the Americas, As stated previously, Whites of the era regarded Africans as subhumans on a par with animals. That distinction separated them from human permutations such as prisoners or servants.
As slaves in Christian America, Blacks were stripped of their humanity and all the accompanying benefits afforded to "humans," including the status of being an immigrant or even the potential of becoming a citizen.
Unlike the White UK prisoners shipped off to Australia wit their humanity intact, African slaves in the Americas were there at the leisure of White men who owned their bodies and subsequently, after years of subjugation, even the minds of many. The UK expatriates sent to Australia were still White human and free.