in a class of its own Definition

class
noun classes

1. A lesson or lecture.

Thesaurus: lecture, seminar, colloquium, lesson.
2. A number of pupils taught together.
(especially US)
3. The body of students that begin or finish university or school in the same year.

Example: class of ‘94
4. A category, kind or type, members of which share common characteristics.

Thesaurus: category, group, type, kind, genre, family, sort, species, order, division, rank.
5. A grade or standard.
6. Any of the social groupings into which people fall according to their job, wealth, etc.

Thesaurus: caste, status, position, standing, lineage, station, sphere, degree, hierarchy, stock.
7. The system by which society is divided into such groups.
8a. colloq
Stylishness in dress, behaviour, etc;
8b. colloq
Good quality.
9. biol.
In taxonomy: any of the groups, eg Mammalia (the mammals), into which a phylum in the animal kingdom or a division (sense 7) in the plant kingdom is divided, and which is in turn subdivided into one or more orders (sense 11).

verb classes, classed, classing

1a. To regard someone or something as belonging to a certain class;
1b. To put into a category.

Thesaurus: categorize, classify, rank, grade, rate, assort, brand, codify, designate.

Idiom: in a class of its own

Outstanding; with no equal.
Thesaurus: unique, unusual, different, one of a kind, sui generis.

Etymology: 17c: from Latin classis rank, class, division.