adjective
necessary to make a whole complete; essential or fundamental.

synonyms
essential, fundamental, basic, intrinsic, inherent, constitutive, innate, structural

adjective
(of a person or action) creating or controlling a situation rather than just responding to it after it has happened.

synonyms
enterprising, take-charge, energetic, driven, bold, dynamic, motivated

noun
the state of being free from illness or injury.

synonyms
good physical condition, healthiness, fitness, physical fitness, well-being, haleness, good trim, good shape, fine fettle, good kilter