Mull over
Definition 1 of 1
Pro Tip 1/3Time Involved
Use when indicating a process of careful thought over time, not a quick decision. 
She needs to mull over her career options for a few days.
Pro Tip 2/3Personal Reflection
Suitable for personal or emotional subjects that require deep consideration. 
I need to mull over how I really feel about this relationship.
Pro Tip 3/3Serious Tone
Often implies the matter is serious and not to be taken lightly. 
The committee is mulling over the implications of the new law.