'alkali-susceptible' originates from Modern English as a compound of 'alkali' and 'susceptible'. 'Alkali' came into English via Medieval Latin and Old Spanish/Arabic, and 'susceptible' derives from Latin 'susceptibilis' through Old French.

'alkali' comes from Arabic al-qaliy (القلَي), meaning 'ashes of saltwort' → Medieval Latin/Spanish/Italian 'alcali/alkali' → modern English 'alkali'. 'susceptible' comes from Latin 'susceptibilis' (from 'suscipere', 'to take up/receive') → Old French 'susceptible' → Middle/Modern English 'susceptible'. The modern compound formed in English by joining the noun and adjective.

Originally 'alkali' referred specifically to the ashes of certain plants used to produce soda; its meaning broadened to denote strong bases/alkaline substances. 'Susceptible' originally meant 'capable of receiving or taking on' and shifted toward 'liable to be affected by'. Combined, the compound now means 'liable to be affected by alkalis'.