I found a graphic here at Textkit of several Roman soldiers. And the following text:
Funditor, milites levis armaturae, legionarii.
so, Funditor is nom, singular meaning “slinger”
milites levis armaturae are genetive(?)
legionarii is also genetive.
the slinger, of the lightly armed legionairs(?)
The only thing is that milites is the nom. plural of miles “soldier”, so there are three labels, labelling, I assume, three different things in the picture. Also, “legionary” rather than “legionair”.
It would appear that the text is split into three parts, each describing a seperate portion of the picture. Thus, there is one slinger (funditor), a group of lightly armed soldiers (milites levis armaturae), and legionaries (legionarii).
“Legionnaire” may be French but it’s also nice in English, too.
Primitùs certè gallicum (seu francicum) vocabulum est “legionnaire”, at nonnè aptum etiam anglicé.