'pistillar' originates from Neo-Latin/Modern formation based on 'pistil' (from New Latin 'pistillum'), ultimately from Latin 'pistillum' meaning 'pestle' (used for pounding).

'pistillar' was formed in English by adding the adjectival suffix '-ar' to 'pistil' (from New Latin 'pistillum'); 'pistil' itself came into English via Medieval/Modern Latin and French from Latin 'pistillum'.

Initially related to the Latin word for 'pestle' (a tool for pounding), the root evolved into the botanical term 'pistil' (the female organ of a flower); 'pistillar' subsequently developed to mean 'relating to the pistil'.