'well-leaved' originates from Modern English, formed from the adverb 'well' and the past-participle/adjectival use of 'leaved' (from 'leaf'), where 'well' meant 'in a good or satisfactory way' and 'leaf' meant 'leaf'.

'leaved' derives from Old English 'lēaf' (leaf) with the adjectival/past-participle suffix '-ed'; 'well' comes from Old English 'wel'. These elements combined in Modern English to produce the compound 'well-leaved'.

Initially it literally meant 'having leaves that are in a good condition' (the literal combination of 'well' + 'leaved'); over time the compound has been used more generally to describe plants that are abundant in or characterized by healthy foliage: 'having abundant or healthy leaves'.