'algal-inhibiting' is a compound from 'algal' + 'inhibiting'. 'Algal' derives from Modern Latin 'alga' meaning 'seaweed' with the English adjectival suffix '-al'; 'inhibiting' comes from Latin 'inhibēre' (to hold in, restrain) via Medieval/Modern Latin and Middle English 'inhibit'.

'algal' formed in English from the Modern Latin noun 'alga' to describe seaweed-related things; 'inhibit' entered English from Latin 'inhibēre' (through Medieval Latin/Old French influence) and produced the present participle 'inhibiting'. The compound 'algal-inhibiting' is a recent technical formation (20th–21st century) used in scientific and industrial contexts.

The component parts originally signified 'seaweed-related' (alga) and 'to hold back' (inhibēre); together they evolved into the modern technical meaning 'having the property of preventing algae growth'.