impressionlessimpressionless

Impressionless comes from Latin impressiō ‘push, thrust, assault, onslaught’, from imprimō ‘to press, impress’, and ultimately from premō.

1. Latinc. 75 BCE–200 CEpremō¹‘to press, push, press close or hard, oppress, overwhelm’
2. Latinc. 75 BCE–200 CEimprimō¹‘to press, impress’
3. Latinc. 75 BCE–200 CEimpressiō¹‘push, thrust, assault, onslaught’
4. Old Frenchc. 842–1400impression¹
5. English1500–presentimpression¹
6. Englishtodayimpressionless¹

1. ¹ Wiktionary, English impressionless

Earlier history uncertain. See Wiktionary.