not a bit—not at all; not in the least:
- I haven’t slept all night and I am not a bit tired.
not a little—to a considerable extent:
- They were not a little surprised to see me, and not a little annoyed either.
Note: The expression does not fully correlate in meaning with the phrase no little—
1. (followed by a noun) much:
- It requires no little care and patient investigation to arrive at a correct conclusion.
2. = not a little:
- Both were deeply interested, immensely impressed, and no little surprised by what they saw.