If you are under the thumb, you are completely controlled by someone else. This control is easily recognised by others but not necessarily by you.
His girlfriend won’t let him go to watch any football matches on Saturdays. He’s totally under the thumb.
If you are all thumbs, you are very clumsy and you keep dropping things. Your hands fail to do their job properly. You might be suffering from nerves or fear or you might just be very tired.
I was all thumbs when I was paying for my shopping and I dropped my money everywhere.
A rule of thumb is a general rule or principle that is based on experience rather than on scientific evidence.
As a rule of thumb, I check the oil levels in my car on the first Saturday in every month.
This means that I try to check the levels of oil in my car once a month and I try to do it on the first Saturday of each month. In practice, I might check the level of oil at different times of the month.
When we tweak something, we change tiny details until it is perfect or as we want it.
Once she had written her letter of complaint, she spent an extra hour tweaking it so that there would be no misunderstanding.
Sometimes we start doing something and realise that what we have done is not up to standard. It is possible to alter what you have done but often it is preferable to start again from the beginning – this is starting from scratch.