Her letter was filled with heartfelt invocations for the family to reunite soon.

invocations 是名词 invocation 的复数形式。invocation 由前缀 in-（表示"向内"）和词根 voc（意为"声音、呼唤"）加上名词后缀 -ation 组成，字面意思是"向内呼唤"，引申为"祈求、祷告"的意思。在句中指"恳切的请求或祈祷"。