### Clue: Soldiers, by not speaking about it at first, able to withstand disappointment (9)
### Answer: RESILIENT 
 ### Explanation: Definition: able to withstand disappointment
 RE($$R$$oyal $$E$$ngineers,soldiers in the British army) ***plus***(by) [SILENT(mute,not speaking) ***containing***(about) I{initial letter of(at first) "it"}].
Answer:  Able to bounce back after,withstand disappointment.