'lactase-promoting' is a compound formed from 'lactase' and the present-participial form of 'promote'. 'lactase' originates from New Latin, built from 'lact-' meaning 'milk' and the enzyme-forming suffix '-ase'. 'promote' originates from Latin 'promovere' ('pro-' forward + 'movere' to move).

'lactase' was coined in scientific New Latin to name the enzyme acting on lactose; 'promote' came into English from Latin promōvere (via Old French/Medieval Latin forms) and developed in Middle English into the modern verb 'promote', with 'promoting' as its present participle; combining them produced the modern compound 'lactase-promoting'.

Originally, 'promote' literally meant 'to move forward'; over time its sense broadened to 'encourage or increase'. 'lactase' has consistently referred to the enzyme that breaks down lactose. The compound now means 'encouraging the activity or production of lactase'.