After days of thinking and recollecting I found this photo of my son near a huge poster made of STICKERS. Some words on the "tree" can be also considered as STEMPS because they were produced using special STAMPS 😁. This is a decoration on the wall of a hall at one of schools.
@olgavita/a-tree-of-knowledge-photochain
So, my words are: STICKER - STAMP - WALL