cross wire vs cross hair

cross wire and cross hair both are nouns.

Word	Noun	Adjective	Verb	Adverb
cross wire	Yes	No	No	No
cross hair	Yes	No	No	No

As nouns, cross wire and cross hair are synonyms defined as:

cross wire and cross hair: either of two fine mutually perpendicular lines that cross in the focus plane of an optical instrument and are used for sighting or calibration

cross wire (noun)	cross hair (noun)
either of two fine mutually perpendicular lines that cross in the focus plane of an optical instrument and are used for sighting or calibration	either of two fine mutually perpendicular lines that cross in the focus plane of an optical instrument and are used for sighting or calibration