Entry 3 senses Webster, 1913

Therewith

· There·with · IPA /ðɛəˈwɪθ/

01 adv. With that or this.

1.
With that or this.
2.
In addition; besides; moreover.
“To speak of strength and therewith hardiness.” — Chaucer.
3.
At the same time; forthwith.[Obs.]