1 deep, unfathomable, abstruse, recondite, arcane, esoteric, intricate, knotty, involved, tricky, inscrutable, indecipherable, cabbalistic, incomprehensible, obscure, subtle, occult, secret, cryptic, puzzling, enigmatic, mystifying, mysterious:
Some aspects of the theory of thought are even too profound for many specialists
2 learned, scholarly, intellectual, erudite, discerning, astute, sagacious, sage, wise, penetrating, sharp, keen, insightful, analytical, knowledgeable, informed, well-informed, well-read:
Russell was one of the most profound thinkers of his day.
3 deep, great, intense, sincere; heartfelt, keen, acute, utter, extreme, overpowering, overwhelming:
He gave a profound sigh and fell asleep at once. It is with profound regret that I must tender my resignation
4 utter, complete, total, perfect, absolute, thorough, thoroughgoing, out-and-out, downright, consummate; awful, terrible:
Her casual attitude stems from her profound lack of awareness of how important the work is. I was immediately struck by the profound silence in the house. Profound changes are under way.