What Does `pugnacious` Mean?

Ready, willing and able to fight.  A hard and tough foe.

Quarrelsome, belligerant, ready for a fight.  Having a combative or ferocious nature.  Truculent.  Although truculent might be interpretted as a bit more savage or cruel than pugnacious.  Pugnacious is more ready to resort to violence, than mindlessly going for you no matter what.

A fish that fights with all it's heart to stop from being reeled in,  and then still tries to bite the fisherman even after it's on the boat and gasping to breathe, that's pugnacious.

Pugnacious means "aggressive or belligerent." A pugnacious person is tenacious, insensitive and tough by virtue of past experience. Such an individual has very less fear and is highly aggressive in nature. He can even resort to force or violence to get his way through.  The word "pugnacious" is believed to have entered popular English literature in the later half of the 16th century.
The synonyms of the word "pugnacious" are bellicose, argumentative, confrontational, combative, hostile, militant, quarrelsome, contentious, attacking, warlike etc.  Just like a diamond becomes hard by going through the grind and fire, a pugnacious person develops a heartless and tough attitude after going through the woes and the injustice meted out to him in life. Here is an example of the word "pugnacious" in a sentence:
'I wonder what was going through the mind of that pugnacious beast of a man who resorted to terrorism to free his country.'

Combative in nature