adds vagueness and indirectness
Attaches to certain question words, quantity expressions, or phrases to create a vague, indirect, or non-specific nuance. Not freely productive; common in fixed expressions like それとなく, 何となく, and 幾度となく.
See also: それとなく · なんとなく · 幾度となく
He indirectly observed her state.
Somehow I feel good today.
I warned him many times, but he didn't listen.
somehow; vaguely; for some reason
time after time; countless times; many a time
on countless occasions; many a time; time and again
in various ways; in many ways; kindly
Derived from the particle と plus the negative form of the verb なく (from ない), literally 'without being that'. The exact historical development is uncertain, but it functions as a suffix adding vagueness or indirectness.