Knightly means of knights, or more often like a knight: brave, honourable, and careful with people who are weaker. You might hear knightly courage, knightly manners, or knightly armour. It is a rather old, bookish word; everyday English is more likely to say brave, noble, or chivalrous. As an adverb it is even rarer: to behave knightly. Though actually, the warm glow around the word is a later feeling. Long ago this family of words could mean a young man or even a servant, so knightly did not always sound grand. Today, if you call someone's behaviour knightly, you are praising it, often a little romantically.