One for the “You learn something new everyday” file is the origin(s) of the word bank. There are at least two etymologies for the modern word, depending on the meaning (at least according to the Oxford English Dictionary).
The first is Middle English banke from Old Norse banki meaning ‘ridge’. This is the meaning found in embankment, usually a man made earthen mound, and perhaps the bank on the side of a river. This Old Norse word comes from Germanic *bankon which is probably related to Germanic *banki-z ‘bench’.
The second etymology is also Germanic but actually came in to English via Late Latin *bancus, via Norman French baunk. In this case, “bank” means “bench”, but because the bench is where the money handlers sat in the market, “bank” also came to mean the house of financial transactions in French, Spanish (banco) and Italian.
The bench meaning can be seen in French banquette and uses such as a “bank of oars” (where the rowers sat). Although the French/Spanish roots came from Late Latin *bancus, it seems likely that the Romans borrowed from a Germanic speaking group (i.e. *banki-z) … which is the ‘bench’ root.
As for bench – this is the *bank-iz ‘bench’ root becoming *benkr (an umlauted form), then going some of Anglo-Saxon phonology, specifically the palatalization process where Germanic /k/ becomes /č/ in some contexts. This is similar to the palatalization which resulted in church” (English) versus kirk (Scots).
What we have is not just a “doublet”, but a “triplet” where we have one route, *banki-z going through three routes to end up in modern English – the native route, via Latin and via a sister Germanic language (Old Norse).
Besides the trivia factor, there are some lessons to be learned here when reconstructing other languages. One is that roots can bounce back and forth between neighbors, not just between “unrelated” languages like Latin & English, but closer relatives like Old Norse and English. Fortunately, we have the written records and modern language to trace some of these elements, but…
The other lesson is that the native root (bench) is the one which the most sound changes have occurred and now looks the least like the original root. When checking a new group of languages, similar looking words could lead to a common root, but it can just lead to a root which has been borrowed a lot.
Documenting sound changes can help track when roots entered a language, and sometimes the “oldest” words are the ones that sound or look the oddest.