full arm's length; from shoulder to fingertip
Refers to the length of the entire arm, from the shoulder to the tip of the middle finger. Often used in contexts like measuring reach or describing a large gesture.
He welcomed me with open arms.
The cloth is about the length of a full arm.
Compound of 大 (おお, 'big') + 手 (て, 'hand/arm'), with rendaku voicing of て to で. The literal meaning is 'big arm', referring to the full length of the arm.