Dotterel, whimbrel, kestrel, scoundrel

The suffix these words share is of such antiquity that the OED is rather tentative in deriving it from the French suffix -eau/elle, an analogous wide-ranging diminutive. The problem is that, whereas some examples like kestrel are straightforward borrowings from Old French, others are not:

Further formations within English on bases not of Romance origin appear in Middle English (e.g. GANGREL n., DOGGEREL adj., DOTTEREL n., MONGREL n., SUCKEREL n.); also, in some cases where the base is of Romance origin, it is uncertain whether the suffixed word was borrowed or formed independently in English (compare COCKEREL n., the equivalent of which is apparently rare in Anglo-Norman and Middle French (Normandy) and not otherwise attested in continental French).

(In many of these cases, even "kestrel," no one knows quite what the current form is a diminutive of.) What the surviving words of this class -- except mongrel -- seem to share is a quaint prettiness, no doubt due to their antiquity, that's nevertheless very disproportionate to what they mean. For instance "whimbrel" meant "little whimperer," and "dotterel" -- the prettiest of the lot -- meant "little dotard," a puzzling name for a bird until you learn that it was "A species of plover (Eudromias morinellus): so called from the apparent simplicity with which it allows itself to be approached and taken." Beyond this it gets messier: e.g., "mackerel" does not have anything to do with "a popular tradition that the mackerel assisted in the sexual activity of the herring" (?!), nor is a scoundrel a little trouble("scunner")-maker. 


By the way, a "ketterel" -- an obscure Scots word meaning "wretch" -- is not to be confused with the eminent physicist, one of many reasons why I'm grateful that my spell-checker does not use the OED.