'arilli' originates from Latin, specifically the word 'arillus', where 'arillus' meant 'a small skin' or 'a little rind' (a covering associated with a seed).

'arillus' (Latin) passed into botanical Latin and English botanical usage; the Latin nominative plural form 'arilli' has been retained in some technical contexts as the plural of 'arillus' (and thus appears in English texts as 'arilli').

Initially, it meant 'a small skin or rind (around a seed)'; over time the term came to denote the fleshy or membranous appendage or covering associated with certain seeds, and 'arilli' is used as its plural in technical contexts.