とも無(な)くAbsentmindedly, Mindlessly, Unconsciously, Without paying attention

ともなく and ともなしに are structures used to indicate that (A) was being done absentmindedly when (B) happened. It will be translated as 'unconsciously (A) when (B)', or 'without paying attention to (A), (B)'.

This pattern is a combination of the case-marking particle と, the adverbial particle も, and the conjunctive form of the い-Adjective ない. It will be seen after the dictionary form of verbs, and can be thought of as literally meaning something similar to 'even while not intending to (B), while (A), (B)'.

ともなしに is similar, but pairs the noun なし 'without' with に, instead of using the conjugative form of ない.

ともなく and ともなしに will often be seen in sentences that use たら. This puts emphasis on the specific time that something happened while performing another action absentmindedly. Despite translating this way, the action that precedes ともなく itself will be intentional, but the thing that comes about as a result of performing that action will not be what the doer was aiming to achieve.