What does 'condescending' exactly mean?

I'm really confused about the meaning of the word 'condescending'. Online dictionaries define it as bossy/disdainful, which fits with...

One woman felt that I was a little condescending toward whites, that I sounded like I was superior.

But I find other usages where being condescending is obviously considered a good thing, perhaps more like being humble, or equal, rather than superior...

He took a condescending and friendly interest in the common people.

(and here are over 1200 more instances of "condescending and friendly" in Google Books)

What's going on? Does this word really have two almost opposite meanings?

For this one the etymology is useful.

It's a Latin word, formed with the prefix con- (meaning 'with') plus the verb descendere (meaning 'go down, descend'), and together meaning to lower oneself metaphorically in status by associating with inferiors.

This is Classical Roman culture, remember; it featured a rigidly enforced vertical social hierarchy, with rich nobles at the top, slaves at the bottom, and everybody else in between.

In Modern English, with a somewhat different social system — and extremely different social values — the word has come to mean not so much to treat everyone alike — which is now a good thing, after all — but rather to be perceived to be making an effort to treat everyone alike, especially one's presumed "inferiors".

Since this is a matter of interpretation, often by those who feel condescended to (note the Passive of an intransitive verb with a transitivizing preposition, like insist on), condescension is easy to complain about, but very hard to distinguish from personal dislike.

In modern Western usage, the word has a strictly negative connotation due to an egalitarian conception of relationships. In the past, the word could be used in a positive sense when a person of higher status was willing to introduce a high degree of mutuality into their relationships with people of lower status.

The Christian hymn "Come Christians, Join to Sing", which was written in Scotland in 1843 but is still widely used, includes an example of this positive usage:

"He is our Guide and Friend; To us He’ll condescend; His love shall never end. Alleluia! Amen!"

The idea that particular verse is conveying is that the Divine Person is willing to enter into relationship with created, mortal beings.

Condescension, like sarcasm, is most often conveyed in body language and tone of voice rather than the content of a message. It can be perceived when it is not (consciously ) intended, and can remain unperceived even where it is deliberate and intentional.

It is nowadays generally taken to mean talking down to your audience, though in bygone times it was not a perjorative term, but rather a positive one.