brains
n. uncountablen. the person in a group who is the most intelligent or does all the planning. You use this when one person is clearly the smartest member of a team.
n. the most intelligent member of a group, especially the one responsible for planning or organizing a collective effort. Informal in register; typically used with the definite article.
She is the brains behind the whole operation.
While the others handled the physical labor, he was the brains of the group and managed the finances.
The investigation revealed that the youngest sibling was actually the brains of the criminal enterprise, orchestrating every detail from a remote location.
Typically used as a singular concept despite the plural form; almost always preceded by 'the'.
He is the brain of the projectHe is the brains of the projectWhen referring to the smartest person in a group, the word must be plural ('brains').