avuncular

Not all uncles are likeable fellows (Hamlet's murderous Uncle Claudius, for example, isn't exactly Mr. Nice Guy in Shakespeare's tragedy), but "avuncular" reveals that, as a group, uncles are generally seen as affable and benevolent, if at times a bit patronizing. Avuncular derives from the Latin noun avunculus, which translates as "maternal uncle," but since at least the 1830s English speakers have used "avuncular" to refer to uncles from either side of the family or even to individuals who are simply uncle-like in character or behavior. And in case you were wondering, "avunculus" is also an ancestor of the word uncle itself.