Unique, a.
Etymology: [F. unique; cf. It. unico; from L. unicus, from unus one. See One.]
Being without a like or equal; unmatched; unequaled; unparalleled; single in kind or excellence; sole. -- U*nique"ly, adv. -- U*nique"ness, n.
1 other Webster entry under this spelling
Unique, n.
A thing without a like; something unequaled or unparalleled. [R.] The phenix, the unique pf birds. De Quincey.
Shades of meaning
Fernald has no entry of its own for unique; he lists it under queer, rare.
Where he writes about it:
Unique is alone of its kind; rare is infrequent of its kind; great poems are rare; "Paradise Lost" is unique. — from rare