Palmeira vs. palma
The difference between palmeira and palma lies in whether you are talking about the entire plant or specific parts/actions. Palmeira refers to the tree itself, while palma usually refers to the palm of the hand, a palm frond, or applause.
Palmeira
B1This word refers to the palm tree as a whole plant. If you are looking at a tree with a tall trunk and large leaves at the top in a tropical setting or garden, you use palmeira.
O vento forte derrubou a palmeira antiga.
(The strong wind knocked down the ancient palm tree.)
Ela decidiu plantar uma palmeira no quintal.
(She decided to plant a palm tree in the backyard.)
Aquela palmeira é muito alta para escalar.
(That palm tree is too tall to climb.)
A palmeira imperial é um símbolo do jardim botânico.
(The imperial palm tree is a symbol of the botanical garden.)
Nós descansamos na sombra da palmeira.
(We rested in the shade of the palm tree.)
Palma
B1This word has three main uses: it refers to the inner surface of the human hand, a single leaf (frond) of a palm tree often used in decorations, or, when used in the plural, the act of clapping hands.
Ela estava segurando uma moeda na palma da mão.
(She was holding a coin in the palm of her hand.)
A plateia bateu palmas com entusiasmo.
(The audience clapped enthusiastically.)
No domingo, eles levaram uma palma para a igreja.
(On Sunday, they took a palm frond to the church.)
Ele suava frio na palma das mãos.
(He was sweating cold sweat on the palms of his hands.)
Peço uma salva de palmas para o nosso convidado.
(I ask for a round of applause for our guest.)
Summary
Use palmeira when referring to the tree growing in the ground. Use palma when referring to the inside of your hand, a specific leaf, or the sound made by clapping.