in- + let(verb)

inlet (1200-1300) Because it lets water in

source: By No machine-readable author provided. Buckeye~commonswiki assumed (based on copyright claims). - No machine-readable source provided. Own work assumed (based on copyright claims)., CC BY-SA 3.0

1. a small arm of the sea, a lake, or a river.: 海、湖、川の小さな河口

入り江; 瀬戸

2. a place or means of entry: 入る場所、入る方法

供給用パイプ, 注ぎ口, 引き入れ口 (↔ outlet)

e.g. an air inlet.: 給気口

e.g. a water inlet: 給水管

3. (chiefly in tailoring and dressmaking) an inserted piece of material.: (主に仕立てやドレスメーキングで)差し込まれた生地

Middle English (denoting admission): from in + the verb let1.