積む
つむ · tsumu · JLPT N3 · verb-godan
to pile up
🧱🌾 Tsumu sounds like two more: you stack two more on the pile
The kanji 積 pairs 禾 (grain) with 責, which mainly gives the sound. The original sense was piling up harvested grain. Today it covers any stacking: 荷物を積む means to load luggage, and 経験を積む means to build up experience.