Thin, slender, slim, slight, tenuous, rare are in general referable not only to measure in width or amount but also to quantity or quality and agree in meaning not broad, not thick, not abundant, nor dense.
Thin basically implies comparatively little extension between two surfaces of a thing or the comparatively small diameter of a cylindrical or nearly cylindrical thing in proportion to its height or length.
In its extended senses the term usually implies the lack of the flesh or substance that fills out a thing to its normal or usual extent and gives it fullness, richness, substantiality, compactness, or density.
Slender , as applied to the bodies of men and of animals, implies leanness or spareness without any suggestion of gauntness or lankiness and usually carries a distinct connotation of gracefulness and of good proportions.
Slender is preferred to thin in describing things of narrow extension when the thinness is an element of beauty and gracefulness of line.
In its extended use slender is often employed with little distinction from thin , but it is often preferred when quantity or amount rather than quality is stressed.
Slim differs little from slender when applied to the figures of persons or animals; it may sometimes suggest fragility or gauntness rather than grace, and lack of flesh rather than excellent proportions.
In its extended senses, however, slim usually carries a clearer implication of meagerness or scantiness than slender , which, though it suggests smallness in amount or quantity, implies less commonly than slim a falling short of adequacy or sufficiency; thus, slim resources are by suggestion more meager than slender resources.
Slight through most of its variations in meaning carries a more obvious implication of smallness than of thinness; when applied to persons, it seldom suggests height or length, as slender usually does or slim sometimes does.
When applied to things, it is often derogatory and usually implies a failure to come up to a level of what is commensurate, adequate, or significant.
Tenuous basically implies extreme thinness or even absence of perceptible thickness; the term is literally applicable to things (as lines, cords, or wires) of great length or height and of minute diameter or to fabrics and textiles which are exceedingly sheer or gauzy.
In its extended senses tenuous often describes something which covers an expanse but lacks density, compactness, or solidity or something which is so finespun or so fine-drawn as to be exceedingly subtle, abstruse, or visionary.
Rare in the sense of rarefied (see also INFREQUENT CHOICE ) is applied chiefly to gases and especially to air. In its uncommon extended use it suggests tenuity or sometimes extreme exaltation or elevation.