die Handfläche
palm
The inner side of the hand, located between the wrist and the fingers.
Er legte die Münze in ihre offene Handfläche.
He placed the coin in her open palm.

palm
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palm
The inner side of the hand, located between the wrist and the fingers.
Er legte die Münze in ihre offene Handfläche.
He placed the coin in her open palm.

This word is simply made up of 'die Hand' (the hand) and 'die Fläche' (the surface/area). So it literally describes the flat inner side of the hand.
Das Kind malte mit Fingerfarben auf seine Handfläche.
The child painted on his palm with finger paints.
Pay attention to the difference between dative and accusative. 'In der Handfläche' (in the palm; dative) describes a position, while 'in die Handfläche' (into the palm; accusative) describes a movement or direction.
Sie hielt einen kleinen Stein in der Handfläche.
She held a small stone in her palm.
Common verbs used in connection with 'die Handfläche' (the palm) are 'etwas in die Handfläche legen' (to place something in the palm), 'mit der Handfläche über etwas streichen' (to stroke something with the palm), or 'sich auf die Handfläche stützen' (to support oneself on the palm).
Sie strich sanft mit der Handfläche über den Kopf der Katze.
She gently stroked the cat's head with her palm.
fist
'die Faust' and 'die Handfläche' are both parts of the hand, but they do not mean the same thing. A fist is formed when you close your hand and curl your fingers tightly inward. The palm is the inner, open side of the hand. It is easy to confuse the words because, in a fist, the fingers are pressed toward the palm. The important point is: with an open hand, you can see the palm; with a closed hand, you have a fist.

Herr Weber hielt die Handfläche unter kaltes Wasser, weil er sich verbrannt hatte.
Mr. Weber held his palm under cold water because he had burned himself.
Nach dem Streit ballte Laura die Faust, sagte aber nichts.
After the argument, Laura clenched her fist but said nothing.