How do you draw "big" when big is an idea, not a thing? The scribes drew a person facing you, arms stretched as wide as they can go — the gesture every child makes when saying "THIS big!". Ideas made visible: that is the second great trick of Chinese writing.
A piece of culture
Everything great is 大 Chinese reaches for 大 the way English reaches for "great": a university is 大学 ("great learning"), an embassy is 大使馆 ("great envoy's house"), yesterday's big news is 大新闻. Even China's beloved panda is 大熊猫 — "the great bear-cat".
Use it in a real word
大人
dàrén · daai6 jan4
adult — literally "big person", exactly how a child would say it