adverb
Used with a negative verb to express that something has never happened or is not at all the case. Emphatic and somewhat literary.
彼からはついぞ連絡がない。
I have never heard from him.
そんな話はついぞ聞いたことがない。
I have never heard such a story.
全然 is a common adverb for 'not at all', but ついぞ carries a stronger sense of 'never' over a long period.
The origin is uncertain; it may be a contraction of an older emphatic expression. The kanji 終 (end) is likely an ateji for the sound.