Where does the term "to sock away s.t" originate?

Solution 1:

OED first attests 'sock' ("also with away", colloquial, "orig[inally] U.S.") in the sense of "put (money) aside as savings" in 1942, and Etymology Online echoes that date for the sense. Etymology Online speculates that the phrase arose "from the notion of hiding one's money in a sock".

A newspaper search finds two mentions of hiding or stashing money in a sock in 1891. The Austin American-Statesman (Austin, Texas) of 17 May 1891, page 2 (paywalled), mentions the proverbial sock in a blurb:

It is said there are about $2,100,00 left jingling about in the toe of Bill Wortham's old sock away back in the corner of the vault.

The Atlanta Constitution (Atlanta, Georgia) 26 Jul 1891, page 21 (paywalled), records a mention of the practice in a speech:

I would rather get my pocket change from an old sock hid away under my own roof, than to give it in order that those other fellows might grow fat.

In 1893, a colloquial use of the verb phrase, with "away", appears in story dialog on page 2 of the 25 Sep Detroit Free Press (Detroit, Michigan; paywalled):

"Anything more than a million is vexation of spirit. I'd just sock that away and cover up sins with the rest."

While not strictly evidence that the use of the verb in the given sense arose from the practice of hiding or keeping money in a sock, the mentions of the practice followed by the appearance of the verbal sense do suggest that origin.