Fiber content tag is missing. Fabric appears to be wool or a wool blend based on texture and construction..  

Hickey Freeman Sport Men’s Button-Up Overshirt Tagged Size Medium.

Charcoal gray Hickey Freeman Sport long-sleeve shirt / overshirt constructed from a substantial wool fabric. 

Features a full button front, point collar and single button-flap chest pocket.

Brand: Hickey Freeman Sport
Size: Fit's More Like a Men's Size Small.
Color: Charcoal Gray
Style: Button-Up Overshirt / Shirt Jacket

Approximate measurements:

Pit to pit: 20.5"
Length: 27.5"
Sleeve: approx. 30–31" from mid neck.

Very good pre-owned condition with light normal wear. 

Please review all photos carefully for exact condition and measurements.