This is the 564th most frequent Chinese word.
光
"Light" or "radiance."
In this sentence, '光' refers to 'light' or 'shine' as a physical phenomenon emitted by the sun.
阳光照亮了大地。
Sunlight illuminates the earth.
Here, '光' is used as an adverb meaning 'only' or 'just.'
我们光喝茶了，还没吃饭。
We only drank tea and haven't eaten yet.
In this context, '光' serves as a complement meaning 'completely used up' or 'none left'.