Painless
“Painless” 是形容词，本义为“没有疼痛的”，如无痛注射；引申义指过程“轻松顺利、毫不费力”，如 “a painless upgrade”（无痛升级）。在医疗、软件更新、手续办理等语境中都很常见。
- “The dentist promised a painless procedure.” (牙医保证这次治疗不会疼。)
- “Switching to the new app was surprisingly painless.” (换用新应用出乎意料地顺利。)
- “She made the interview feel painless with her warm smile.” (她温暖的笑容让面试变得轻松不少。)
“Painless” 由 “pain”（疼痛）与 “-less”（没有）构成，“-less” 源自古英语，表示“缺乏、无”。
“-less” 为否定后缀，加在名词后构成形容词，如 hopeless、careless；本词即“无疼痛的”。
在英语广告与医疗宣传中，“painless” 是高频卖点词；科技语境里常形容迁移、升级“零痛感”，强调用户几乎无感知。
- 固定搭配: “painless procedure” (无痛手术/流程), “painless transition” (顺利过渡)
- 名词: painlessness
- 副词: painlessly
“pain + less”：少了 pain，就是 painless——不疼、也不费劲。
“The upgrade took ten minutes and was completely painless; nobody even noticed the server had restarted.” (升级只花了十分钟，完全无感；甚至没人注意到服务器重启过。)