One definition for the adjective "barbarous" is "characterized by the occurrence of barbarisms" (M-W).
Barbarisms have been defined as:
"the practice or display of barbarian acts, attitudes, or ideas"
"an idea, act, or expression that in form or use offends against contemporary standards of good taste or acceptability"
While I can readily understand what it means for a sentence or paragraph to be "barbarous," I often have trouble comprehending what it means for a word to be less than well-formed or barbarous. John Stuart Mill asserts that the Latin word ENTITAS (from ENS) is barbarous like its English counterpart "entity."
ENTITAS is a neologism based on the present participle of ESSE (the Latin form of the verb "to be"). I'm not sure what makes ENTITAS or "entity" barbarous, but maybe a classicist or linguist can help with this question.