当下[dāng xià]
词典immediately：立即，马上；直接地；紧接地。
词典instantly：立即，马上，立刻；马上地；即刻地；立即地。
词典当下
词典at once：立刻；立即；同时；一起。
（立刻） instantly; immediately; at once:
例：我一听这话，当下就警惕起来。
Hearing this, I was instantly on the alert.