[The Squatter of Amon Rûdh]

Tolkien's linguistic puns and games are indeed a fascinating feature of his writing. Unfortunately most of those jokes require explanation for the likes of us to understand them, so extensive was his philological learning. The following are examples of which I'm particularly fond.

Writing about The Hobbit for an English newspaper, Tolkien explained the origin of Smaug's name:

The dragon bears as a name - a pseudonym - the past tense of the primitive Germanic verb Smugan, to squeeze through a hole: a low philological jest.

(Letter #25, to the editor of the Observer)

Then there's the case of the Withywindle. The following is from Shippey's J.R.R. Tolkien: Author of the Century, and follows a quotation of the passage from The Old Forest that describes the river.

If Tolkien had left his study in Northmoor Road, walked back to the University Parks, crossed the 'Rainbow Bridge', and then walked along the other side of the river away from the town of Oxford in the direction of the villages of Wood Eaton and Water Eaton - as no doubt he did - he would have seen virtually the same sight: the slow, muddy, lazy river fringed with willows. The real river, the one that flows into the Thames at Oxford, is the Cherwell. The Oxford Dictionary of English Place-Names gives a different derivation, but Tolkien was always capable of rejecting the advice of Oxford dictionaries. I think he derived the name from Old English *cier-welle, the first element coming from cierran, 'to turn to': so, 'the turning stream', 'the winding stream', which is what the Cherwell is... Further down the Thames, furthermore, is Windsor, which may take its name from *windels-ora, 'the place on the winding stream'. Finally, withy is simply the old word for 'willow', frequent in English place-names, like the Warwickshire Withybrook. The Withywindle is a combination of the Cherwell itself, and words for its two main features, its willows and its slowly-twisting course.