What does "quantum" mean?

Quantum: (Math.) A definite portion of a manifoldness, limited by a mark or by a boundary. W. K. Clifford. Quantum meruit ( Etym: [L., as much as he merited] (Law), a count in an action grounded on a promise that the defendant would pay to the plaintiff for his service as much as he should deserve. -- Quantum sufficit (, or Quantum suff. Etym: [L., as much suffices] (Med.), a sufficient quantity. -- Quantum valebat ( Etym: [L., as much at it was worth] (Law), a count in an action to recover of the defendant, for goods sold, as much as they were worth. Blackstone.