未知
みち · michi · JLPT N1 · na-adj
not yet known
未 = not yet + 知 = know; same sound as 道 (road), an unexplored road
未 means not yet and 知 means know, so 未知 literally means not yet known. Its reading michi is also the word for road (道), a handy hook: the unknown is a road you have not travelled yet.
未 — tree 木 with extra short top stroke
未 originally pictured a tree with luxuriant new branches at the top, suggesting tender shoots not yet matured. From this 'not yet ripe' image it came to mean 'not yet' or 'have not.' It is also the 8th Earthly Branch, used in the traditional sexagenary cycle.