Baby bouncer? (4)
I believe the answer is:
knee
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">baby bouncer?</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 knee that I've seen before include "joint input" , "Human joint" , "Major joint in leg" , "Leg bender" , "It jerks reactively" .)