Reading 森鴎外 Mori Ōgai I’m getting used to finding words and phrases that are almost or even entirely unique to Mori’s oeuvre. It turns out that Google doesn’t understand Mori either. When I wanted to know how frequent the use of 威福 was outside of Mori, I looked for 威福 -辞典 -辞書 -森 -鴎外 and was surprised to see that I still got 62,100 hits. Not so. Google currently doesn’t seem to know that 威福 is actually a word and pulls the characters apart. When I looked for "威福" -辞典 -辞書 -森 -鴎外 (with quotes around 威福) I got only 370 hits, again underlining Mori’s unusual choice of words. According to Google only about 99 pages used 威福 without being a dictionary or a reference to Mori (most are historical texts).
Normally even cryptic and uncommon words get around 50,000 hits in Japanese. Only really obscure, archaic and obsolete expressions plummet down to about 500 hits (not counting dictionaries). Archaic words like 紅毛船 or 胤裔 get about 500 hits. However, while 威福 as an expression seems unused, its basic meaning can hardly be missed, since the separate characters are very much in use. 威 is suggestive of 威力 (‘power’) or 威圧 (‘coercion’) and 福 can only mean ‘wealth’. And in combination with 擅にする (‘act selfishly’) - as Mori uses it - its implied meaning of ‘using one’s power or wealth to make people do one’s wishes’ is easily guessed as well.