These words refer to a good or superlative physical or mental state. Healthy at its most neutral may refer to an absence of illness; at its most positive it refers to normal or excellent functioning: a recovery that left him perfectly healthy provided he doesn’t over-exert himself; healthy minds in healthy bodies. Well and healthy are the most common of these words, if not the most informal, but well is more nearly restricted to the neutral implications of healthy rather than its positive ones: asking the doctor when she would be well again. Sound is much more positive in tone, although strictly speaking it can refer simply to an absence of illness or defect, like well : an alertness and liveliness that marked the baby from the beginning as having an unusually sound constitution. Fit is similar to both well and sound in the sense of good physical condition as well as absence of illness or defect.

• The champion should be fit again in two or three weeks.

Strong takes up this slant, emphasizing powerfulness of physique or forcefulness of mind, although these qualities may be possessed by someone who is not healthy or well : strong athletes laid low by polio; Ruskin’s strong mind becoming increasingly shadowed by mental illness.

The remaining words stress exclusively the side of healthy that refers to excellent functioning. Robust adds to the emphasis of strong implications of positive health as well: robust warriors who were never sick a day in their lives; a robust personality able to triumph over every adversity. The word also has overtones of full-bodied zestfulness, manly eagerness and ampleness of appetite: the robust and sometimes ribald songs of sailors; a robust interest in the opposite sex. Hearty concentrates mostly on these last aspects of robust , indicating an active expression of high spirits and the satisfaction of desire: a hearty appetite; living to a hearty old age. Here, a sexual connotation possible for robust is more clearly present, although the word is more often restricted to refer to men: the hearty camaraderie of most stag parties.

Vigorous refers to forcefulness, like strong, adding to this a note of positive well-being: rosy cheeks and sparkling eyes that spoke of vigorous good health; a closely reasoned theory that revealed a vigorous mind at work. The word, however, is completely lacking in those connotations of robust and hearty that refer to masculine appetite: the vigorous skill with which her poems are written. Hale would suggest excellent functioning, although strictly it pertains to absence of illness or defect. In any case, the word sounds archaic, and except in stock expressions is not often used nowadays: hale and hearty .