Oak-to-be (5)
I believe the answer is:
acorn
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">oak-to-be</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for acorn that I've seen before include "Baby oak?" , "Nut of oak tree" , "oak's fruit" , "From which a "tall oak" may grow" , "Potential oak" .)