Elderliness or the mental and physical infirmity resulting from this: Jim's aunt seemed to be suffering from senility since she was physically frail and continually worried about falling and breaking an arm or a leg.

Forgetting names and faces or misplacing keys are normal occurrences for any age and when people are young, they think nothing of such situations; however, as they get older, they're tempted to worry that such actions are signs of senility.

The onset of the characteristics of declining at an earlier than normal time in a person's life: Jane's father, who was only in his 40s, had to be moved into a nursing home as a result of his premature senility because he couldn't take care of himself anymore and he needed more attention than his family could provide.

Mental disorders which may be associated with becoming old: The psychoses of senility often involves the inability to deal with social situations or consists of behavioral disorders.

More severe psychosis of senilities may include confusion, memory failure, disorientation, restlessness, and speech disturbances.