score:1

You can increase a width of the labels:

"yAxis": [...,
    {
        ...
        "title": {
            ...,
            style: {
                width: '200px'
            }
        }
    }
]

Live demo: http://jsfiddle.net/BlackLabel/eb4g6rtc/

API Reference: https://api.highcharts.com/highcharts/yAxis.title.style


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