To Add Something
transitive verb, godan verb
たす
足す (たす) To Add Something
足りる (たりる) To Be Enough, To Be Sufficient, To Suffice
足りない (たりない) Not Enough, Insufficient, Not Sufficient
足し算 (たしざん) Addition
加える (くわえる) To Add, To Include
足す is used for adding numbers and things. 加える seems to only be used for adding things.