If you are looking for a descriptive usage dictionary, then you’ve hit the mother lode. This reference book should be within easy reach on your desk whenever you’re working into US English. Don’t be fooled by bad online reviews describing this dictionary as an attempt at giving the all-clear to the ‘anything goes’ faction. It’s not a prescriptive work and, as such, it delves into the history of words and phrases, while letting you, the writer, choose which option to follow based on context and the information it provides. Take the ahold entry for example: M-W does not sanction or legitimize its use overtly. Rather, it seems to merely suggest that the one-word spelling calls attention to itself. A sensible editor will therefore intuit that it should give this word a miss in carefully edited prose. End of story.