slow-acting

The compound adjective 'slow-acting' is a transparent modern English formation. Its first element, 'slow', descends from the Old English 'slāw', which carried connotations of mental and physical sluggishness, a meaning retained in its core sense of low speed. The second element derives from the Latin verb 'agere', meaning to drive or do, which entered English via Old French as 'act'. The present participle form '-acting' indicates the ongoing performance of this action. Combined, the term literally describes something that "acts slowly," a logical and descriptive construction used primarily in technical and medical contexts to denote a delayed effect or response.

Structure: slow (adjective) + acting (present participle) - slow: From Old English 'slāw' (inactive, sluggish). Germanic origin. Functions as an adjective describing a low speed or rate. - acting: From the verb 'act', from Latin 'agere' (to do, drive). The '-ing' suffix forms the present participle, here used adjectivally to mean "performing an action".