• 拡大かくだい — enlargement / magnification
• 拡張かくちょう — expansion / extension
• 拡声器かくせいき — loudspeaker / megaphone
• 拡散かくさん — diffusion / spread
• 拡充かくじゅう — expansion (esp. in capability or function)
• 拡幅かくふく — widening (of a road, etc.)
• 拡張子かくちょうし — file extension (computing)

拡 combines the radical 扌 (“hand”) with the phonetic 広 (“wide”), showing the image of making something wider by hand — extending, enlarging, or spreading out. It appears frequently in technical, social, and geographic contexts.