Latin ăcĭcŭlātus ‘furnished with needlelike or bristlelike spines’. Presumably for the “conspicuous and formidable” glochids.
Eggli & Newton (Etymological Dictionary of Succulent Plant Names. 2004) translate the epithet as “marked with fine irregular streaks” (“application obscure”), but that meaning does not seem applicable here.
Opuntia aciculata. Image credit: Frank Vincentz / CC BY-SA 3.0
Maarten H.J. van der Meer (2022 Sep 17). Opuntia aciculata. Dictionary of Cactus Names. Retrieved from https://www.cactusnames.org/opuntia-aciculata