Strong, stout, sturdy, stalwart, tough, tenacious can all mean having or manifesting great power or force (as in acting or resisting).
Strong , the most inclusive of these terms, fundamentally implies the possession of great physical power and may connote such varied causes as sound health or physical size and vigor or soundness of construction and substance, but in extended use it may apply to groups whose force is dependent upon numbers, organization, or discipline or to a spiritual or mental power or faculty that acts with force and vigor or to some very potent or powerful thing or to something (as color or light or emotion or sentiment) that is particularly intense or violent.
Stout (see also FLESHY ) carries a stronger implication than does strong of an ability to resist aggression or destructive forces or of an ability to endure hard use, severe pain, or great temptation without giving way. When applied to persons, it often suggests resolution, doggedness, or fearlessness.
When applied to things, stout usually also suggests solid, substantial construction or a texture that resists stress or strain.
In fact the term is generally applicable when the suggestion of power to resist or endure is more emphatic than that of a power to do or to effect.
Sturdy implies qualities in inanimate as well as in animate things that suggest the possession of rugged health; the term carries no suggestion of powers derived from such qualities as size, intensity, or vehemence but connotes rather an inner strength typically derived from healthy vigorous growth, close solid construction, or a determined spirit that gives it staying power and stoutness.
Stalwart usually implies strength derived from what is so deeply established or firmly rooted that it is unassailable or impregnable or is completely dependable.
When applied to persons with reference to their physique or prowess, stalwart regularly suggests great strength, but it often throws the emphasis upon heroic build or largeness of frame.
Tough suggests the strength that comes from a texture or a spirit that is firm and unyielding and effectively resists attempts to pierce, destroy, or overcome; it stresses hardiness rather than vigor, resistant elasticity or wiriness rather than hardness or solidity, or a capacity for yielding that is just sufficient to increase rather than to destroy a person’s or thing’s strength or stoutness.
Tenacious comes very close to tough in its most general implications, but it places greater emphasis upon retentiveness of what has been gained or of adherence to a support, position, or idea; it carries a strong suggestion of holding on, of adhesiveness, or of maintaining strength or position in spite of all opposing forces that would dislodge, dispossess, thwart, or weaken.
When applied to material things and especially to substances it may suggest a powerful clinging quality and extraordinary resistance to forces that tend to effect separation or pulling apart.
When applied to persons it suggests a stubborn hold upon something (as a possession or an opinion) that defies the efforts of others to break.