stack - pile up - be filling Today, I have learned some words same meaning. At first I felt complexity then after be study, I feel quite interesting : 1. stack : I aware this word usually appear in game ( dota ) that i often play. In game, When the items stack each other that mean they can't be used together such as they are overlapped to each other. 2. pile up : look and hear then this word like as "pipe'' but mean of them very difference. ''pile up'' mean to arrange in stacks. 3. be filling : I link this word with "full". It's used to make full something :)