noun
Refers to a military, expedition, or operational base. Also used in compounds like 宇宙基地 (space station).
アメリカ軍は沖縄に基地を持っている。
The US military has a base in Okinawa.
南極観測基地から中継です。
We are broadcasting from the Antarctic research base.
noun, used as a suffix
Internet slang suffix derived from キチガイ (crazy person). Attaches to nouns to mean 'someone obsessed with X'. Often written in katakana as キチ. Humorous and informal; can be derogatory.
彼は本当にゲームキチだよね。
He's a total game freak, isn't he.
ネットでよく見る「○○キチ」ってどういう意味？
What does '○○キチ' that you often see online mean?
The original derogatory term meaning 'crazy person'. 基地/キチ is a softened, slangy suffix derived from it, used humorously or self-deprecatingly.
Sense 1 is a standard Sino-Japanese compound (基 'foundation' + 地 'land'). Sense 2 is a slang abbreviation of キチガイ (crazy person), reanalyzed with the kanji 基地 or written in katakana.