Lair (3)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lair</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for den that I've seen before include "Animal's home or gent's study" , "Hidden lair of an animal" , "Wild animal's home" , "Animal's lair or man's study" , "Hiding place" .)
(Other definitions for pen that I've seen before include "Put down" , "See 20" , "Confine the writer" , "Animal enclosure" , "Writing tool" .)