well-nigh

adverb

policing the coastline all the time was well-nigh impossible:

almost, nearly, just about, about, more or less, practically, virtually, all but, as good as, next to, close to, near, nigh on, to all intents and purposes, approaching, bordering on, verging on, nearing;

roughly, approximately;

not quite;

informal pretty nearly, pretty much, pretty well.

well-nigh Oxford Dictionary of English