Month Before Last, The Month Before Last
noun
The previous previous month (remember that 々 just repeats the kanji before it) is the month before last.
せんせんげつ
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
先々月、キューバにいきました。
I went to Cuba the month before last.
先々月、フロリダで大きなハリケーンがあったそうだ。
There was a big hurricane in Florida the month before last.
先々月のレシートを見て下さい。
Please look at the receipt from the month before last.