borisyankov/DefinitelyTyped — pull request #285 by Steve-Fenton (2013-02-15 10:01:30+00:00)
Title: Update highcharts/highcharts.d.ts

The documentation for the xAxis: http://api.highcharts.com/highcharts#xAxis

Suggests the same for the xAxis options - it is an object not an array.