This is the 151st most frequent German word.
gar
"Gar" in German means "cooked" or "done" (in the context of food).
In this sentence, 'gar' is used to emphasize the negation of the statement.
Das ist gar nicht so schwierig.
That is not difficult at all.
Here, 'gar' intensifies the sense of the negative question, suggesting surprise.
Hast du gar keinen Hunger?
Are you not hungry at all?
'Gar' is used to accentuate the totality or entirety of the effort made, conveying an idea similar to 'even.'