一つ
ひとつ · hitotsu · JLPT N5 · noun
one (thing)
1️⃣ hito (one, as in hitori = one person) + tsu (the generic thing counter)
Native Japanese counting: hito- is the old root for one, also heard in hitori (one person). The -tsu ending is the general counter for things, shared by futatsu (two) and mittsu (three). So hitotsu = one + thing.
一 — single horizontal stroke
一 is one of the simplest pictographs in Chinese, depicting a single horizontal line to represent the number one. It has retained essentially the same form since oracle bone script over 3,000 years ago. By extension it also means 'first,' 'whole,' or 'same.'