Definition of "assistant"
(obsolete) Someone who is present; a bystander, a witness.
Quotations
a woman of great authority, having first yeelded an accompt unto her Citizens, and shewed good reasons why she was resolved to end her life, earnestly entreated Pompey to be an assistant at her death, that so it might be esteemed more honourable […].
1603, Michel de Montaigne, chapter 3, in John Florio, transl., The Essayes […], book II, London: […] Val[entine] Simmes for Edward Blount […]