window pane vs back breaker

window pane and back breaker both are nouns.

Word	Noun	Adjective	Verb	Adverb
window pane	Yes	No	No	No
back breaker	Yes	No	No	No

As nouns, window pane and back breaker are synonyms defined as:

window pane and back breaker: street name for lysergic acid diethylamide

Other synonyms of window pane include acid, battery-acid, dose, dot, Elvis, loony toons, Lucy in the sky with diamonds, pane, superman, Zen.

window pane (noun)	back breaker (noun)
street name for lysergic acid diethylamide	street name for lysergic acid diethylamide