• 減少げんしょう — decrease / reduction
• 削減さくげん — cut / curtailment
• 軽減けいげん — mitigation / alleviation
• 半減はんげん — halving / reduced by half
• 節減せつげん — economizing / saving
• 減税げんぜい — tax reduction
• 減収げんしゅう — decrease in revenue
• 減退げんたい — decline / ebb

減 combines the water radical 氵 with 咸 (phonetic giving ゲン), evoking the sense of something diminishing—like water receding or lessening.

Common in political, financial, and daily contexts: population decrease, budget cuts, tax reductions, etc.

人口じんこうが 減へっています。
The population is decreasing.

ムダを 減へらす 方法ほうほうを 考かんがえましょう。
Let’s think of ways to reduce the waste.