Explanation
Expresses doing something unintentionally or without conscious thought.
Formation
Verb-dictionary form + ともなしに + Verb
Detailed explanation
VerbるともなしにVerb is used to show that you do some action without particularly intending to. Often you ‘end up doing’ something by habit or casually.
Examples
Hon o yomu tomonashi ni nemutte shimatta.
I ended up falling asleep while reading the book without really meaning to.
Karui kimochi de tegami o kaku tomonashi ni, kare ni honshin o kokuhaku shita.
While writing a letter casually, I ended up confessing my true feelings to him.
Sanpo o suru tomonashi ni, atarashii kafe o mitsuketa.
While I was walking with no particular destination, I found a new cafe.
Youfuku o seiri suru tomonashi ni, mukashi no shashin o mitsuketa.
As I was absentmindedly organizing clothes, I came across some old photos.
Practice
Grammar content sourced from hanabira.org.