goiter vs goitre

goiter and goitre both are nouns.

Word	Noun	Adjective	Verb	Adverb
goiter	Yes	No	No	No
goitre	Yes	No	No	No

As nouns, goiter and goitre are synonyms defined as:

goiter and goitre: abnormally enlarged thyroid gland; can result from underproduction or overproduction of hormone or from a deficiency of iodine in the diet

Other synonyms of goiter include struma, thyromegaly.

goiter (noun)	goitre (noun)
abnormally enlarged thyroid gland; can result from underproduction or overproduction of hormone or from a deficiency of iodine in the diet	abnormally enlarged thyroid gland; can result from underproduction or overproduction of hormone or from a deficiency of iodine in the diet