Related Clues:

• Treehouse underpinning
• Flipper, e.g.
• Bird perch
• Tree part
• Owl's perch
• Don't go out on one
• It comes out of a trunk
• Tree branch
• Extremity
• Tree appendage
• Swing support, perhaps
• An arm and a leg
• Life partner?
• Arm, e.g.
• Wing, perhaps