This is the 3964th most frequent Russian word.
заметил
"Noticed" or "remarked."
In this instance, "заметили" conveys becoming aware of unnoticed or obscure details after closely reviewing the object or context in question.
Мы не сразу заметили ошибки в отчете.
We didn't immediately notice the mistakes in the report.
The word "заметил" is employed here in the sense of realizing or perceiving a change in the surrounding environment after paying attention to it.
Я заметил, что на улице стало прохладно.
I noticed that it became cooler outside.
Here, "заметила" denotes observing or recognizing something visually without necessarily commenting on or elaborating upon it.