When stone holds jade within, the mountain itself takes on a glow.
Tips
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yùn is literary - you will meet it only in classical citations and high-register modern writing. Two famous loci: Lu Ji's 《文赋》 'Rhapsody on Literature' - 石韫玉而山辉 'stone holding jade gives the mountain its glow' (a metaphor for hidden talent). And Confucius in the Analects - 韫椟而藏 'to store [a jade] in a cabinet and hide it' (waiting for the right buyer / patron). Both phrases live on as set classical references in modern essays about talent and patience.
memory
Read the components: 韦 (originally an enclosure, here suggesting 'wrapped, enclosed') + 昷 (warm / soft, supplying the sound yùn through wēn-yùn variation) = 'kept warm and wrapped inside' = to contain, to hold within.
Left 韦 - the indexing radical (Kangxi #178). Originally feet walking around an enclosure, later 'tanned leather'. Here it carries the 'wrapped / enclosed' image: a thing wrapped up, kept inside. Same radical groups 韬 (sheathe), 韫 (contain) - both about hiding or wrapping.
Right phonetic 昷 - supplies the sound (wēn to yùn, a regular shift in the same phonetic series). The same phonetic anchors 温 (warm), 瘟 (epidemic), 蕴 (store up - semantic twin of 韫).
