a chemical group or functional group (the part of a molecule responsible for certain properties; often appears in compounds like 'functional group')
この分子にはアルコール基（-OH）が二つある。
This molecule has two hydroxyl groups (-OH).
官能基は分子の反応性を左右する重要な基だ。
Functional groups are the parts of a molecule that determine its reactivity.
化学式を書くとき、基の位置を明確に示すことが重要だ。
When writing chemical formulas, it's important to indicate the positions of groups clearly.
(free) radical — an atomic group or radical that can exist independently or as a reactive species
紫外線の作用で遊離基が生成されることがある。
Free radicals can be generated by the action of ultraviolet light.
抗酸化物質は遊離基の働きを抑える役割を持つ。
Antioxidants serve to suppress the activity of free radicals.
a counter for installed or mounted objects (e.g. stone lanterns, gravestones, satellites) — used to count units that are set up or installed
庭に石灯籠が三基置いてある。
There are three stone lanterns placed in the garden.
この寺には古い供養塔が五基ある。
This temple has five old memorial towers.
人工衛星を二基打ち上げた。
Two satellites were launched.