Radical 广 (broad, shelter) over the phonetic 郭 — and 郭 itself meant 'outer city wall.' So 廓 = the wide outer enclosure, hence both 'outline/contour' (轮廓 lúnkuò) and 'vast/wide-open' (寥廓 liáokuò 'boundless,' 廓清 kuòqīng 'to sweep clean').
register
Bound form — almost never stands alone. Most common compound: 轮廓 (lúnkuò, contour/outline).
