Kleenex vs tissue

Kleenex and tissue both are nouns.

Word	Noun	Adjective	Verb	Adverb
Kleenex	Yes	No	No	No
tissue	Yes	No	Yes	No

As nouns, tissue is a hypernym of Kleenex; that is, tissue is a word with a broader meaning than Kleenex:

Kleenex: a piece of soft absorbent paper (usually two or more thin layers) used as a disposable handkerchief
tissue: a soft thin (usually translucent) paper

Other hypernyms of Kleenex include tissue paper.

Kleenex (noun)	tissue (noun)
a piece of soft absorbent paper (usually two or more thin layers) used as a disposable handkerchief	part of an organism consisting of an aggregate of cells having a similar structure and function
	a soft thin (usually translucent) paper

Kleenex (verb)	tissue (verb)
	create a piece of cloth by interlacing strands of fabric, such as wool or cotton