Learner's definition of MENTAL
1 a : of or relating to the mind b : existing or happening in the mind
We had a mental image/picture of what we thought the house would look like.
I've got a mental list of the things I need at the store.
I'll make a mental note to see if we can reschedule the meeting.
mental arithmetic [=arithmetic done in your mind without writing numbers or using a calculator]
always used before a noun
2 a : relating to or affected by an illness of the mind b : caring for people with mental illnesses