deep

modif.

1. Situated or extending far down

   low, below, beneath, profound, bottomless, submerged, subterranean, submarine, inmost, deep-seated, rooted, deep-rooted, abysmal, extending far downward, fathomless, sunk, deep-set, subaqueous, immersed, dark, dim, unfathomed, impenetrable, buried, inward, underground, underwater, downreaching, of great depth, depthless, immeasurable, yawning; see also under 1.

   Antonyms shallow*, near the surface, surface. *

2. Extending laterally or vertically

   far, wide, broad, yawning, penetrating, distant, thick, fat, spread out, to the bone*, up to the hilt*; see also broad 1, extensive 1, long 1.

   Antonyms narrow*, thin*, shallow. *

3. Strongly felt

   intense, heartfelt, sincere, profound; see intense.

4. *Difficult to penetrate or understand

   profound, abstruse, mysterious, recondite; see difficult 2, profound 2.

5. Low in pitch

   bass, deep-toned, sonorous, rumbling; see bass. See syn. study at broad.

go off the deep end*

1. go to extremes, go too far, lose one's good sense, rant; see overdo 1, rage.

2. have a breakdown, lose control, become irresponsible, become insane;

in deep water