The action reading. Covers four overlapping senses: answer (回应, 应答), comply (应邀, 答应), handle (应付, 应对), and fit/apply (应用, 适应, 反应). All trace to one root: actively meeting something with a matching action.
mistakes
Two compounds neutralise the second char to toneless ying in spoken Mandarin: 答应 (agree) and 照应 (look after). Note 照应 keeps the full falling tone when it means 'correspond to' - same characters, different sense, different tone.
Same shelter radical as the yīng reading - the split is phonological, not graphic. 广 indexes the char under Kangxi #53.
semantic
⺍xiǎo
three small strokes (graphic residue)
Compressed remnant of traditional 應's falcon-and-heart interior. The yìng reading derives from the same etymology - a trained falcon responding to its handler's call - preserved here only as graphic residue.
