Sailplane (6)
I believe the answer is:
glider
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sailplane</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that sailplane can be written as glider)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for glider that I've seen before include "Motorless plane" , "taking flight?" , "Plane supported by air" , "Unpowered plane" , "Kind of aircraft without an engine" .)