c. 1600, "loss or impairment of the qualities proper to the race or kind," also figurative, "descent to an inferior state," from French dégéneration (15c.) or directly from Late Latin degenerationem (nominative degeneratio), noun of action from past-participle stem of Latin degenerare "to be inferior to one's ancestors, to become unlike one's race or kind, fall from ancestral quality," used of physical as well as moral qualities, from phrase de genere, from de "down from, away from" (see de-) + genus (genitive generis) "birth, descent" (from PIE root *gene- "give birth, beget").
[Degeneration] means literally an unkinding, the undoing of a kind, and in this sense was first used to express the change of kind without regard to whether the change was to perfect or to degrade; but it is now used exclusively to denote a change from a higher to a lower kind, that is to say, from a more complex to a less complex organisation; it is a process of dissolution, the opposite of that process of involution which is pre-essential to evolution. [Henry Maudsley, "Body and Will," 1884]
c. 1600, "single, solitary," from French unique (16c.), from Latin unicus "only, single, sole, alone of its kind," from unus "one" (from PIE root *oi-no- "one, unique"). Meaning "forming the only one of its kind" is attested from 1610s; erroneous sense of "remarkable, uncommon" is attested from mid-19c. Related: Uniquely; uniqueness.
late 14c., "group of people, animals, etc.; kind or variety of person or animal," from Old French sorte "class, kind," from Latin sortem (nominative sors) "lot; fate, destiny; share, portion; rank, category; sex, class, oracular response, prophecy," from PIE root *ser- (2) "to line up."
The sense evolution in Vulgar Latin is from "what is allotted to one by fate," to "fortune, condition," to "rank, class, order." Later (mid-15c.) "group, class, or category of items; kind or variety of thing; pattern, design." Out of sorts "not in usual good condition" is attested from 1620s, with literal sense of "out of stock."