This is the 6338th most frequent Chinese word.
成日
"成日" means "all day long" or "constantly."
In this sentence, '成日' is used to describe something that happens frequently or habitually, indicating a consistent pattern of behavior.
他成日都忘记带钥匙。
He always forgets to bring his keys.
Here, '成日' implies a sense of prolonged duration throughout the day for the activity mentioned, emphasizing a negative habit.
她成日看电视，不读书。
She spends all day watching TV and doesn't study.
This instance illustrates how '成日' characterizes continual activity, especially when describing a playful or energetic state.