What does it mean to describe someone's chin as "pugnacious"?

If one were to describe someone's chin as "pugnacious", what would that chin look like?

EDIT: In the context where I read it, it was used as a purely physical description I believe; it wasn't situation-specific. Therefore, I don't think it means simply thrust out.

Solution 1:

What an odd way to describe a chin.

Pugnacious: inclined to quarrel or fight readily; quarrelsome; belligerent; combative.

So this would be the type of chin that belongs a habitual fighter. I think it would be pushed out, assuming an aggressive stance. The jaw would be set firmly, which is also aggressive, and I imagine most strongly that it would be square.

Square-jawed seems to describe pugnacious kinds of people, but I don't have a ready link for this. I'll see if I can find some.

Here we go:

From Paradise pursued: the novels of Rose Macaulay

Solution 2:

The description you found was of American portraitist, Gilbert Stuart:

For the impulsive, unreliable Stuart, who left a trail of incomplete paintings and irate clients in his wake, George Washington emerged as the savior who would rescue him from insistent creditors. "When I can net a sum sufficient to take me to America, I shall be off my native soil," he confided eagerly to a friend. "There I expect to make a fortune by Washington alone. I calculate upon making a plurality of his portraits. . . and if I should be fortunate, I will repay my English and Irish creditors." In a self-portrait daubed years earlier, Stuart presented himself as a restless soul, with tousled reddish-brown hair, keen blue eyes, a strongly marked nose, and a pugnacious chin. This harried, disheveled man was scarcely the sort to appeal to the immaculately formal George Washington.

Here's the self-portrait referred to in the passage (hardly a pugnacious chin, I think):

Here's a later portrait of him by Charles Willson Peale (not sure how his nose line changed so much, but the chin's a bit more pugnacious)

Ah, here we go. Pugnacity!

By the way, describing chins as pugnacious is much more common than I thought. And pugnacious jaw is even more common.

Edit:
One piece I think is missing from the other answers is why pugnacious might mean jutting or square-jawed. I found this at Etymonline:

pugnacious 1640s, from L. pugnacis, gen. of pugnax "combative," from pugnare "to fight," from pugnus "fist" . . .

So, I posit that a pugnacious chin is square because it is shaped like a fist.

Solution 3:

The word pugnacious comes from the Latin pugnare ("to fight"). So in normal usage means belligerent or ready to fight.

To apply that to someone's chin is quite subjective. I would imagine it to be pushed out forward in an agressive manner.