Latin word Senex which means old is the base upon which senile is built .Other words associated with senex are senior (older member) ,senate (council of old (wise & experienced ) members ).
1. Showing a decline or deterioration of physical strength or mental functioning as a result of old age or disease.
2. Of or belonging to old age or aged persons
3. Pity or compassion
Most of you would have heard of Nile River in Egypt. Nile valley civilization is one of the oldest civilizations. Word Senile contains nile .So we can associate River Nile to the word senile.
Another way is to associate word senile with word senior which is commonly used .Senior means old member so we can associate senile to old age .
1. His somewhat senile mind was striving for forgotten memories.
2. The Senile Tiger Was Shot Down.
3. Although the old man was well over 90, he did not show even a trace of senility.