As a glance at the history of the language will show, English is derived from a Germanic language — Old English, in fact, is thoroughly Germanic in its forms, structures, and vocabulary. But around the year 1100, English saw an influx of words from French (which is a romance language, i.e., derived ultimately from Latin); and in the Renaissance, words by the thousands were imported directly from Latin.
For this reason, English is today a mongrel language, mixing Germanic and latinate roots. Often we can find pairs of words, near synonyms, of which one comes from an Anglo-Saxon root and one from a latinate root. Sometimes, in fact, we have three closely related words, one each from Anglo-Saxon, from Latin via French, and directly from Latin, as in kingly (Germanic), royal (from French roi), and regal (from Latin rex, regis).
As a (very rough) general rule, words derived from the Germanic ancestors of English are shorter, more concrete, and more direct, whereas latinate words are longer and more abstract: compare, for instance, the Anglo-Saxon thinking with the Latinate cogitation.
Most of our vulgarities are of Anglo-Saxon ancestry: compare, for instance, shit (Germanic) with excrement (latinate).
Note: This guide is still in the early stages of development.
Three question marks mean I have to write more on the subject. Bear with me.