adj. 1 extensive, bottomless, abyssal, unfathomable, profound; wide, broad, yawning, chasmal or chasmic All our supplies were lost in a deep crevasse in the glacier 2 profound, arcane, recondite, difficult, abstruse, obscure, esoteric, incomprehensible, beyond or past comprehension, impenetrable, unfathomable, inscrutable, mysterious, mystic(al), occult, weighty, serious, Colloq heavy Religious philosophy is too deep a subject to discuss at breakfast 3 wise, learned, sage, sagacious, astute, perspicacious, profound, discerning, acute, intense, penetrating, knowledgeable, knowing Margaret is one of the deepest thinkers on the subject 4 rapt, absorbed, engrossed, occupied, preoccupied, intent, intense, involved, engaged, immersed, lost, Colloq into Don't disturb him when he's deep in thought 5 devious, cunning, shrewd, crafty, canny, clever, knowing, scheming, artful, designing He thinks there is a deep plot against him 6 profound, intense, sincere, serious, heartfelt, earnest, ardent, fervent, poignant, deep-rooted I know of your deep concern for her 7 low, resonant, booming, resounding, sonorous, rumbling The deep sound of thunder rolled across the valley 8 rich, dark, intense, strong The sky was a deep blue
n. 9 the deep. the ocean, the main, the sea, the waters, the high seas, the briny (deep), the wave(s), Davy Jones's locker, Neptune's or Poseidon's kingdom or domain It was midnight on the waters and a storm was on the deep
adv. 10 deeply, far down, profoundly, intensely, earnestly, heavily We drank deep of the cooling liquid