ferreted out

Osam Dazaiの小説 "The Setting Sun" (Donald Keen訳)を読んでいます。

I extracted the bedding from our baggage and helped Mother spread it. Something about her worried me so much that I ferreted out the thermometer to take her temperature.

"ferreted out" は初めてみる表現ではありませんが、今まで取り上げたことが無いようなので今回取り上げます。

・Oxford English Dictionary: to discover information or to find somebody/something by searching carefully and completely, asking a lot of questions, etc.: He is determined to ferret out the truth about what happened.
・Collins Dictionary: If you ferret about for something, you look for it in a lot of different places or in a place where it is hidden.: She nonetheless continued to ferret about for possible jobs.
・Cambridge English Dictionary: to search for something by moving things around with your hands, especially in a drawer, bag, or other closed space: I was just ferreting around in my drawer for my passport.

小動物の "ferret" が動詞になると何故上記の意味になるのか不思議で語源辞書をみました。

Online Etymology Dictionary: early 15c., "hunt with a ferret," from ferret (n.) or from Old French verb fureter, in reference to the use of half-tame ferrets to kill rats and flush rabbits from burrows. The extended sense of "search out, discover," especially by perseverance and cunning, usually with out (adv.), is from 1570s.