Low in pitch (4)
(Other definitions for bass that I've seen before include "Lowest register of the male voice" , "bottom of sound?" , "Fish for the low-voiced" , "Very low - perch" , "Fish (which sings?)" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">low in pitch</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for deep that I've seen before include "greatly involved?" , "Sunk low" , "profoundly" , "Cavernous" , "Intense; low (in pitch)" .)