Other sources of doublets

Source: OED

Phonological

Stress shift

In the following doublets, one form preserves the original word-final stress of (Norman) French, whereas the other reflects the word-initial stress characteristic of Germanic.

In Algeo and Butcher, ch. 9, you'll see some further examples of this source of doublets in connection with the discussion of British vs. American English.

Old stress New stress
an'tique 'antic
ca'det 'caddie

Syncope

Syncope refers to the loss of unstressed medial syllables.

Original form Result of syncope
Augustine Austin
Benedict Benet
courtesy curtsey
fantasy (cf. fantasia) fancy
frenetic frantic
paralysis palsy

We can see the two processes at work in frantic and palsy. First must have come stress shift in frenetic and paralysis, leaving formerly stressed medial vowels vulnerable to syncope.

We also see both processes at work in Chaucer's poetry, where there is variation between old mar-ri-'age vs. new 'mar-r(i)age.

Aphesis

Aphesis refers to the loss of unstressed initial syllables. The term apheresis is also sometimes used for this process.

Full form Result of aphesis
adown down
adub dub
apprentice prentice
attention 'tention!
defense fence
esquire squire

Morphological

Metanalysis

Metanalysis refers to etymologically or grammatically unmotivated morphological (re)segmentation of a linguistic form. Sometimes the form resulting from metanalysis became the standard form; sometimes not.

Sometimes, forms with metanalysis survive as dialect or nonstandard forms, possibly with their own OED entry.

In some cases, metanalysis is attested in the historical record, but did not catch on.

The above cases all arise on the basis of misanalyzing spoken language. With the rise of literacy, such cases have been superseded by ones based on misreading. There's even a special humorous word misles for such cases. Here's a list of misles.

Musical cousins (and some orphans)

Question: Based on the linguistic evidence, what would you guess was the size of the ancestor of the entire family of bowed string instruments?

Demonyms

A demonym, according to the OED, is the "name by which a native or resident of a specific place is known".

Question: What are the demonyms for the following places?

Followup question: And why?

Legalese