In what sense are the quasars quasi-stellar?

Answer 1

A quasar is an abbreviated term for quasi-stellar radio sources.

Quasi - means something resembling or having a likeness to.

Stellar - means pertaining to, or characteristic of stars

The first "quasars" were discovered using radio telescopes in the late 1950s. Many were recorded as radio sources with no corresponding visible object.

So they became known as a radio source resembling something like a star, or quasi-stellar radio sources.

It was not until 1964 when they became known as quasars.

"So far, the clumsily long name 'quasi-stellar radio sources' is used to describe these objects. Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form 'quasar' will be used throughout this paper.

-- Hong-Yee Chiu in Physics Today, May, 1964"

Answer 2

In the early days of radio astronomy, scientists examined normal stars with radio telescopes, and other galaxies, and figured out pretty much what a star or galaxy looked like to a radio telescope. But there were other things, incredibly far away, and looked a little like stars or galaxies, but which were not visible AT ALL with even the biggest Earth-based telescopes. And they weren't really all THAT much like stars; they were too radio-bright to be stars, but too small to be galaxies. They really didn't know WHAT they were.

Whenever we discover something new, we have to come up with a name for it. Because it was visible in a radio-telescope and was sort of like a star (but not really!) they called it a "quasi-stellar radio source". Newspaper reporters are generally clueless about science and that was too long for a headline anyway, so it got abbreviated as "quasar".