Of direct descent (6)
I believe the answer is:
lineal
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">of direct descent</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for lineal that I've seen before include "In a line as, say, a descendant" , "One-dimensional" , "In a straight row" , "In line of descendants" , "Having only one dimension" .)