'algal-stimulatory' originates from Modern English by combining 'algal' and 'stimulatory'. 'algal' derives from New Latin 'alga' (from Latin 'alga'), where 'alga' meant 'seaweed'. 'stimulatory' comes from Latin 'stimulare', ultimately from 'stimulus', where 'stimulus' meant 'a goad or incentive'.

'algal' developed as an adjective form from the noun 'alga' in scientific New Latin and entered English as 'algal'; 'stimulatory' evolved from the verb 'stimulate' + adjectival suffix '-ory', and the compound form 'algal-stimulatory' is a modern compound adjective formed in English scientific usage.

Initially, 'alga' referred simply to 'seaweed' and 'stimulus' meant a 'goad' or 'incentive'; over time these elements combined in scientific English to form a compound adjective meaning 'causing stimulation or growth of algae'.