1.
months (duration)
A counter for counting the duration of time in months. Different from 月 which is used for naming specific months.
ヶ月 counts the duration in months. It's written with the small ヶ character. Common forms include 一ヶ月 (one month), 二ヶ月 (two months), 六ヶ月 (six months - note the っ), 十ヶ月 (ten months). Compare with 月 (for naming months: 一月 = January).