Lush describes plants growing thick, green and healthy — a lush lawn, lush hills, the lush growth after a wet spring. The picture is always of abundance, and always of something living.
From plants it spreads to anything rich and full: a lush sound, lush fabrics, a lush production. That use is approving and slightly luxurious. In British informal speech lush also means simply lovely — that's lush — mainly in Wales and the West Country, and a lush is a different word again, an old and unkind noun for a heavy drinker. Context separates them without effort, but a learner meeting the noun for the first time should know it is not a compliment.
1adjectivelushOf plants, growing thickly and looking green and healthy.
“After the rain the whole valley was lush.”
2adjectiverichRich, full and pleasing to the senses.
“The film has a lush orchestral score.”
3adjectivelovelyIn informal British speech, lovely.
“That cake was lush.”
lush is a quality of growth.
Lush meant slack. Middle English lusch was limp, loose or relaxed, from a Germanic word for weak or feeble, so the sense of thick green growth is a late reversal of the word.
Proto-Indo-European
*lēy- — to let; leave behind
Proto-Germanic
*laskuz
Proto-West Germanic
*laskwī̆
Old English
*lysċ
Middle English
lusch — slack, relaxed, limp, loose
English, today
lush
Built from
From Middle English lusch (“slack, relaxed, limp, loose”), from Old English lysċ, lesċ (“slack; limp”), from Proto-West Germanic laskwī̆, from Proto-Germanic laskuz, laskwaz (“weak, false, feeble”), from Proto-Indo-European lēy- (“to let; leave behind”). Akin to Old English lysu (“false, evil, base”), Middle Low German lasch (“slack”), Middle High German erleswen (“to become weak”), Old Norse lǫskr (“weak, feeble”), Gothic 𐌻𐌰𐍃𐌹𐍅𐍃 (“weak, feeble”), Middle Low German las, lasich (“slack, languid, idle”), Low German lusch (“loose”). a doublet of lusk. More at lishey, lazy.
Etymology from Wiktionary, CC BY-SA
Practised in Nature & Weather, Sharper Adjectives