What does the symbol ≪ mean in word origin description in dictionary.com?
Solution 1:
<< means that one or more links in the etymological chain are supposed but are unattested.
Compare:
x < y means that x is believed to come from y immediately.
x << y means that x is believed to come from y though not immediately, that is, one or more words mediate between x and y but that word or those words have not been identified.
x (<?) < y means that that x is believed to come from y though it is not known whether it does so immediately OR one or more words mediate between x and y.