leash vs tether

leash and tether both are nouns.

Word	Noun	Adjective	Verb	Adverb
leash	Yes	No	Yes	No
tether	Yes	No	Yes	No

As nouns, leash and tether are synonyms defined as:

leash and tether: restraint consisting of a rope (or light chain) used to restrain an animal

Other synonyms of leash include lead.

leash (noun)	tether (noun)
a figurative restraint	restraint consisting of a rope (or light chain) used to restrain an animal
restraint consisting of a rope (or light chain) used to restrain an animal
the cardinal number that is the sum of one and one and one

leash (verb)	tether (verb)
fasten with a rope	tie with a tether