One-dimensional (6)
I believe the answer is:
linear
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">one-dimensional</span>' is the definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for linear that I've seen before include "following straight path" , "Of a line or length" , "In one dimension, I learn (anag.)" , "Long and narrow, of one dimension" , "Measured lengthwise" .)