1 in the past, but not now: --
I went to Disney World once.
Going to the Olympics is a once-in-a-lifetime opportunity (= a rare and valuable one).
4 in the past, but not now: --
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
Môžeme to dokončiť krok za krokom, nech je cesta akokoľvek dlhá a nedá sa dokončiť, nech je cesta akokoľvek krátka, ak si ani neoznačíte svoju stopu.