to brighten one's face, to cheer up: to let a sad look lift into a cheerful one
This is a rare word that pictures light returning to a downcast face. It always appears where someone is grieving and longs, however briefly, to look and feel cheerful again. Three of its four appearances are of this kind, and they clearly belong together: the line in Job 10:20 is almost a direct quotation of the plea in Psalm 39:13, so whatever the psalmist meant, Job means too.
The force of the word is best seen in Job 9:27, where it stands right beside the picture of "laying aside my sad face." To brighten in this sense is to drop the frown and put on a lighter expression. It is not settled contentment but a momentary recovery of cheer, and in Job it is bitterly ironic: he proposes to cheer up and then admits, a breath later, that his dread rushes back.
The nearest everyday word is "cheer up" or "brighten," and a good translation gets the reader most of the way there. What can be lost is the specific image of a face lifting and the fleeting, almost wishful quality of the relief, which is why translations vary between brighten, cheer up, take comfort, and recover. It is a close relative of the ordinary word for gladness (שָׂמַח), but narrower: not general rejoicing so much as a downcast look brightening.