Y vs atomic number 39

Y and atomic number 39 both are nouns.

Word	Noun	Adjective	Verb	Adverb
Y	Yes	No	No	No
atomic number 39	Yes	No	No	No

As nouns, Y and atomic number 39 are synonyms defined as:

Y and atomic number 39: a silvery metallic element that is common in rare-earth minerals; used in magnesium and aluminum alloys

Other synonyms of Y include yttrium.

Y (noun)	atomic number 39 (noun)
the 25th letter of the Roman alphabet	a silvery metallic element that is common in rare-earth minerals; used in magnesium and aluminum alloys
a silvery metallic element that is common in rare-earth minerals; used in magnesium and aluminum alloys