偶然发现，偶然遇到，偶然碰到：无意中找到（某物）或偶遇（某人）。
find unexpectedly
同义词： fall upon / strike / come upon / light upon / come across / chance on / happen upon / attain / discover
... chance to 偶然发生 chance upon 偶然遇见 chance 侧重事前无安排或无准备而发生的事，特指巧合。 ...
...com... chance on偶然发现[遇到]... chance upon偶然发现[遇到]；碰... change hands转手；易手...
come to pass on or occur on（a certain day）适逢 chance upon偶然碰到；偶然发现 meet with（misfortune，disaster，etc．）；encounter遭遇 ..
偶然遇见；偶然发现
Perhaps you might chance upon the dictionary at some old bookstall.
或许你会在旧书摊上偶然发现这本字典。
However it is non official and will be known to people who chance upon it (for now).
然而，它(blog)不是官方的而且将会被碰巧遇到它的人所熟知(对现在来说)。
It happened one day that the son of a king, while riding in the forest, came by chance upon the dwarfs' house and asked for a night's lodging.
有天有件事情发生了，一个国王的儿子，当他骑马来到这个森林，偶尔来到矮人们的房子晚上要求投宿。
It's not every day you chance upon a Sri Lankan British singer with a Kingston-meets-cockney brogue, rapping about revolution.
Then I chance upon DiscVault .
It was, accordingly, declared Germany's first victim, a chance pounced upon by Austria's post-war politicians (many of whom were themselves victims of Nazism).