perhaps; possibly; by any chance
Expresses a conjecture or suspicion, often with a sense of slight doubt or surprise. Commonly used in rhetorical questions or when the speaker is wondering about something unexpected.
I suspected that he might just possibly be the culprit.
Perhaps he has already arrived, hasn't he?
By any chance, did something happen?
Hearing the footsteps, I had a sudden suspicion.
It's possible we might have gotten lost.
ひょっとして is a common spoken equivalent for a sudden hunch, while もしや is more formal or emphatic in tone.
もし means 'if' and introduces a conditional clause, while もしや means 'perhaps' and expresses a guess or suspicion.
Derived from もし (if) + や (old interrogative particle). The combination expresses a tentative conjecture.