Gwen Farrell Adair, best known for her work in the classic TV show "M*A*S*H" ... and, more importantly, for being the first licensed woman boxing referee, has died.

Keith Farrell, her son, tells TMZ ... Gwen died yesterday in Sherman Oaks ... of natural causes.

Gwen appeared on "M*A*S*H" and "Billy Jack" ... but her real legacy began in 1980, when she stepped into the boxing world as a referee -- an unheard of move at the time. Per her family ... she earned the respect of fighters, trainers, and fans alike while she broke barriers.

A GoFundMe has been set up to help the family with funeral and memorial expenses ... the post states in part ... "Her passing leaves a deep void in our hearts, one that cannot be filled. We will miss her voice, her strength, and the quiet comfort she brought into our lives. While we are heartbroken, we are also incredibly grateful for the life she lived and the legacy she leaves behind."

Gwen was 94.

RIP