Place to find a crook (3)
(Other definitions for elbow that I've seen before include "Barge" , "Sharp bend in a road or river" , "Nudging joint?" , "push" , "Reject" .)
(Other definitions for arm that I've seen before include "inlet" , "Body part" , "Shoulder to fingertip" , "Activate fuse" , "What soldiers do" .)