A hundred and fifty years ago ‘guttural’ was in use as a technical term in phonetics, as a descriptor for a place of articulation. In 1869 A.J. Ellis wrote
The guttural nasal seems to have been the regular pronunciation of ng in English.
A helpful note in the OED tells us:
By non-phoneticians any mode of pronunciation which is harsh or grating in effect is often supposed to be ‘guttural’; with this notion the designation is popularly applied by English-speakers to the German ch, but not to k or g, though technically it belongs equally to them. As a technical term of phonetics, the word was first used to denote the Hebrew spirant consonants א, ה, ח, ע; it is now commonly applied (inaccurately, if its etymological sense be regarded) to the sounds formed by the back of the tongue and the palate, as /k/ /g/ /x/ /ɣ/ /ŋ/.(I have supplied the OED’s missing closing bracket in the last sentence, and replaced its wrong symbol ɤ by the correct ɣ. O tempora, o mores!)
As a phonetic term ‘guttural’ has now been entirely supplanted by more precise terms: mainly ‘velar’, but also ‘uvular’, ‘pharyngeal’ and ‘glottal’, as appropriate. The non-technical use of ‘guttural’ has declined in parallel, and has not been replaced by ‘velar’ or anything other phonetic term.
The OED’s first citation for ‘velar’ in the phonetic sense is dated 1876. (Its definition for the noun sense of this word, though, still reads ‘a velar guttural’.)
Here is part of the Google ngram for ‘guttural’ (blue) and ‘velar’ (red). Follow the link to view the whole graph. As you see, the crossover point at which ‘velar’ became more frequent than ‘guttural’ was as recent as the late 1960s. But if we follow the trend lines for 1990-2000 and extrapolate for 2000-2010 we might well find that it has now lost that lead.