prefix
Prefix attached to time words to mean the upcoming one. Common with 年, 月, 週, 学期, etc.
来年の春に日本へ行く予定です。
I plan to go to Japan next spring.
来月の会議の日程を教えてください。
Please tell me the schedule for next month's meeting.
suffix
since; for the past
Suffix attached to time expressions to indicate a duration from a past point until now. Often used with ～年, ～か月, ～週間, etc.
彼は20年来の友人です。
He is a friend of 20 years.
先月来、ずっと雨が降っていない。
It hasn't rained since last month.