Fraco vs. débil
While both fraco and débil translate to weak in English, they are not always interchangeable. Fraco is the general, all-purpose term used in most situations, while débil is more formal and specific, often implying frailty or a constitutional weakness.
Fraco
A2This is the most common and versatile word for weak. It is used in everyday language to describe a lack of physical strength, low intensity or quality (like coffee or a signal), or a lack of force or character (like an argument or a person).
Ele se sentia muito fraco depois da doença.
(He felt very weak after the illness.)
O café desta manhã está muito fraco.
(This morning's coffee is very weak.)
O sinal do Wi-Fi está fraco neste quarto.
(The Wi-Fi signal is weak in this room.)
Seu pulso estava fraco e rápido.
(His pulse was weak and fast.)
Acho que o argumento dele foi bastante fraco.
(I think his argument was quite weak.)
A luz da lanterna ficou fraca de repente.
(The flashlight's light suddenly became weak.)
Débil
B2This is a more formal, literary, or medical term for weak, often translating better as feeble or frail. It suggests a deeper, more inherent or constitutional weakness, frequently related to poor health, old age, or a delicate condition. It is not typically used for objects or concepts like coffee or signals.
O paciente idoso estava muito débil para andar sozinho.
(The elderly patient was too feeble to walk alone.)
Ele tem uma constituição débil desde a infância.
(He has had a frail constitution since childhood.)
Com uma voz débil, ela pediu um copo de água.
(With a feeble voice, she asked for a glass of water.)
A saúde dela ficou débil após a longa enfermidade.
(Her health became frail after the long illness.)
O governo ofereceu apenas uma resposta débil à crise.
(The government offered only a feeble response to the crisis.)
A sua memória para datas sempre foi um pouco débil.
(His memory for dates has always been a bit weak.)
Summary
In essence, use fraco as the default word for weak in almost any everyday context, from physical strength to the quality of a drink. Reserve débil for more formal situations to describe a person who is feeble or frail, especially due to health or age, or to describe an action that lacks force in a more formal or literary way.