understand
- realize
‘understand’
If you can understand someone or can understand what they are saying, you know what they mean.
His lecture was confusing; no one could understand the terminology.
Her accent was hard to understand.
If you say that you understand that something is true, you mean that you have been told that it is true.
I understand he's been married before.
There was no definite evidence, I understand.
‘realize’
Don't use understand to say that someone becomes aware of something. Don't say, for example, ‘Until he stopped working he hadn’t understood how late it was'. You say ‘Until he stopped working he hadn’t realized how late it was'.
As soon as I saw him, I realized that I'd seen him before.