• 汽車きしゃ — train (steam-powered)
• 汽船きせん — steamboat / steamship
• 汽笛きてき — steam whistle
• 汽缶きかん — steam boiler
• 汽力きりょく — steam power
• 蒸汽じょうき — steam (archaic usage)

汽 is made of the water radical and the element 气, symbolizing rising vapor. It refers to water turned into steam, and is commonly used in early transportation terms like trains and boats.

昔むかしは 汽車きしゃで旅たびをしました。
In the past, people traveled by steam train.

汽笛きてきの音おとが鳴なりました。
The steam whistle sounded.