GG5, 新和英中辞典

GG5, distinguishes between 気軽 and 気軽に, with a sub-entry for the latter. The 中辞典 entry is entirely is about 気軽に. I think having the separate entry is appropriate.

@@ -13,1 +13,2 @@
-<gloss>casually</gloss>
+<gloss>readily</gloss>
+<gloss>cheerfully</gloss>
@@ -17,0 +18,1 @@
+<gloss>casually</gloss>

I don't think the definition of 気軽 (carefree; buoyant; 
lighthearted; sprightly) is quite adequate to convey what 気軽
に usually means. Maybe the definition of 気軽 could be 
modified instead -- "casual" seems like a good word to put 
into it.