I came a cross the expression かげぐち【陰口】(backbiting) and found it in my dictionary as follows
人の陰口をきく［たたく］｜[speak ill of a person / run a person down] behind his back / backbite
When I tried to look up the meaning of きく the only transitive verbs that seem possible are 聞く＆ 聴く. However these relate to listening or at best "asking" which does not seem to be quite same thing.
Should I just accept such expressions as idioms? Even if that is the correct course it seems odd that the entry for 聞く does not mention this use.