If you’re okay with a great-circle distance, as mentioned in the comments, then this should work. It’s the haversine distance:

def haversine(origin, destination, units='mi'):
    # Radian deltas
    origin_lat = radians(float(origin[0]))
    origin_lon = radians(float(origin[1]))
    destination_lat = radians(float(destination[0]))
    destination_lon = radians(float(destination[1]))
    lat_delta = destination_lat - origin_lat
    lon_delta = destination_lon - origin_lon

    # Radius of earth in meters
    r = 6378127

    # Haversine formula
    a = sin(lat_delta / 2) ** 2 + cos(origin_lat) * \
        cos(destination_lat) * sin(lon_delta / 2) ** 2
    c = 2 * asin(sqrt(a))
    meters_traveled = c * r

    scaling_factors = {
        "m:": 1,
        "km": 1 / 1000,
        "ft": 3.2808,  # meters to feet
        "mi:": 0.000621371  # meters to miles
    }

    return meters_traveled * scaling_factors[units]

If you already have the geodesic (great circle) distance in meters and you want the chord length, then you can do the following

def chord(geodesic_distance):
    """
    Chord length
    C = 2 * r * sin(theta/2)

    Arc length; which is geodesic distance in this case
    AL = R * theta

    therefore
    C = 2 * R * sin(AL/(2*R))
    """
    r = 6378127  # Radius of earth in meters

    return 2 * r * sin(geodesic_distance / (2 * r))