Several parts combine into one character.

直 combines 十 (ten) with 目 (eye) and an angled stroke beside it — a straight vertical line drawn above an eye (目), carrying the idea "to look straight with ten (十) eyes." From many eyes looking straight came "straight, upright, honest."

Korean hanja-sound "jik": 直線 (jikseon, straight line), 正直 (jeongjik, honesty), 直接 (jikjeop, direct), 垂直 (sujik, vertical), 直角 (jikgak, right angle), 率直 (soljik, frank). Paired with 正 (correct) seen earlier, it forms 正直 (honesty).

Mandarin: zhí, 2nd tone. 直接 (zhíjiē, direct), 一直 (yìzhí, all along / continuously), 直到 (zhídào, right up until), 直播 (zhíbō, live broadcast — "direct transmission"), 简直 (jiǎnzhí, simply / virtually). 一直 (yìzhí, continuously) is an everyday Mandarin essential.

Japanese: on-readings チョク (choku) and ジキ (jiki), kun なお.す (naosu), なお.る (naoru), ただ.ちに (tadachini). 直接 (chokusetsu, direct), 正直 (shōjiki, honest — a ジキ reading), 直る (naoru, to be fixed), 素直 (sunao, obedient / frank), 直線 (chokusen, straight line). 直す (naosu, to fix) is used daily.

Memory aid: a straight line (十) above many eyes (目) — looking straight, hence upright.