'capillary-acting' originates from Latin, specifically the words 'capillaris' and 'agere', where 'capillaris' meant 'of a hair (thin thread)' and 'agere' meant 'to do or act'.

'capillary' entered English via French 'capillaire' from Latin 'capillaris' (from 'capillus' meaning 'hair'), and 'acting' derives from Latin 'agere' through Old English/Middle English forms of 'act'; these elements were combined in modern English to form the compound 'capillary-acting'.

Initially, it referred to something 'relating to hair' or 'hair-like (thin tube)', but over time it evolved into the technical sense 'relating to or operating by capillary action', now used to mean 'acting by capillary action'.