Earth's satellite (4)
(Other definitions for boon that I've seen before include "Blessing, favour" , "Favour, request" , "Godsend" , "Something beneficial - a blessing" , "Benefaction" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">earth's satellite</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for moon that I've seen before include "Remove boxers, maybe" , "who headed a religious 29 [CULT]" , "Idle (around) - satellite" , "Phoebe" , "Daydream - Europa of Jupiter, say" .)