'algae-suppressing' is a modern English compound formed from 'algae' + the present participle 'suppressing' (from the verb 'suppress'). 'Algae' is the plural form of Latin 'alga', borrowed from Greek 'álga' meaning 'seaweed'. 'Suppress' comes from Latin 'supprimere' (from 'sub-' meaning 'under' + 'premere' meaning 'to press').

'algae' entered English as the plural of Latin 'alga' (from Greek 'álga', 'seaweed'). 'Suppress' evolved from Latin 'supprimere' through Old French/Medieval Latin into Middle English as 'suppress', and the present participle form 'suppressing' is used productively to form compound adjectives in modern English (e.g., 'algae-suppressing').

Individually, 'algae' originally referred to 'seaweed' and related aquatic plants, while 'suppress' originally meant 'to press down (under)'; combined in modern usage they mean 'to reduce or prevent algae growth', a specific applied sense used for treatments and materials.