'algal-inhibitory' is a compound formed from 'algal' and 'inhibitory'. 'algal' originates from Latin, specifically the word 'alga', where 'alga' meant 'seaweed'. 'inhibitory' originates from Latin, specifically the word 'inhibere', where 'in-' meant 'in' and 'hibere' (from 'habere' via historical variation) meant 'to hold or keep'.

'algal' developed from Latin 'alga' into scientific English as 'alga' and the adjectival form 'algal'; 'inhibitory' developed from Latin 'inhibere' through Old French/Medieval Latin forms into Middle/Modern English 'inhibit' and the adjective 'inhibitory'; the modern compound 'algal-inhibitory' is a recent scientific formation combining these elements.

Initially, the parts meant 'seaweed' and 'to hold in' respectively; over time, when combined in modern scientific usage they evolved to the current meaning of 'preventing or restraining the growth of algae'.