This is the 14545th most frequent German word.
lehnen
To lean.
The word 'lehne' is used here in the phrase 'lehne ab', which means 'to reject' in the context of refusing an offer.
Ich lehne das Angebot ab.
I reject the offer.
Here 'lehnen' is used intransitively to describe the position of an object being supported against something else.
Das Bild lehnt an der Wand.
The picture is leaning against the wall.
In this sentence, 'lehnen sich' is reflexively used to express the action of a person leaning out.