This is the 13954th most frequent Polish word.
posadź
"Posadź" means "plant" or "seat" (as in to plant a seed or to seat someone).
The word 'posadź' in this sentence is used as an imperative verb meaning 'to sit someone down'. It is a command directed at placing the child on the chair.
Posadź dziecko na krześle.
Sit the child down on the chair.
Here, 'posadź' is used as an imperative verb to instruct the action of planting. Its meaning shifts to 'to plant' depending on the context.
Posadź drzewo w ogrodzie.
Plant the tree in the garden.
In this sentence, 'posadź' is again an imperative verb meaning 'to sit someone or something down'. It conveys the action of placing the cat on the couch.