cross hair vs cross wire

cross hair and cross wire both are nouns.

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

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

cross hair and cross wire: 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 hair (noun)	cross wire (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