The Spanish verb 'flaquear' (to weaken) comes from combining the Spanish adjective 'flaco' (thin, weak) with the verbal suffix '-ear'. The adjective 'flaco' itself derives from the Latin word 'flaccus', meaning 'flabby' or 'weak'. The '-ear' suffix is commonly used in Spanish to form verbs from adjectives or nouns, creating a verb that means 'to become or make something have the quality of the base word'. In this case, 'flaquear' literally means 'to become weak' or 'to show weakness'.

The most obvious related Spanish word is the common adjective 'flaco', meaning 'thin' or 'skinny'. This is a very frequent word in Spanish that beginners often learn early. While 'flaco' primarily refers to physical thinness in modern Spanish, its connection to 'flaquear' reveals its secondary meaning of 'weak' or 'feeble'. Understanding this connection can help remember that 'flaquear' refers to showing or developing weakness.

While there aren't many common English cognates, the English word 'flaccid' (meaning soft, loose, or lacking firmness) comes from the same Latin root 'flaccus'. This connection can help English speakers remember that 'flaquear' relates to becoming weak or losing strength, similar to how something becomes flaccid when it loses its firmness or rigidity.