Countertenor is a coordinate term of contralto.

As nouns the difference between contralto and countertenor

is that contralto is the lowest female voice or voice part, falling between tenor and mezzo-soprano. The terms contralto and alto refer to a similar musical pitch, but among singers, the term contralto is reserved for female singers; the equivalent male form is counter-tenor. Originally the contratenor altus was a high countermelody sung against the tenor or main melody while countertenor is adult male singer who uses head tone or falsetto to sing far higher than the typical male vocal range.