Through And Through Meaning

(idiomatic) Completely; entirely; fundamentally.

Example:   He moved from Cincinnati to San Francisco, but he's still a Cincinnati Bengals fan, through and through.
1898, J. Meade Falkner, Moonfleet Chapter 4
  Thus, sitting where I was, I lit my candle once more, and then clambered across that great coffin which, for two hours or more, had been a mid-wall of partition between me and danger. But to get out of the niche was harder than to get in; for now that I had a candle to light me, I saw that the coffin, though sound enough to outer view, was wormed through and through, and little better than a rotten shell. So it was that I had some ado to get over it, not daring either to kneel upon it or to bring much weight to bear with my hand, lest it should go through.