Shortly means soon — not this second, but not long from now. The doctor will see you shortly; the train will be arriving shortly; I will be with you shortly.
You hear it in announcements, waiting rooms and careful emails far more than at the kitchen table, where soon does the same job with less starch. Its other big use is with after and before, pinning one event beside another: he left shortly after nine, she died shortly before her ninetieth birthday. Then there is a meaning that catches people out — to answer shortly is to answer curtly, in a sharp few words, because you are annoyed. 'Fine,' he said shortly. The company tells you which one you have: with a future verb it is time, with a verb of speaking it is temper.
1adverbshortlyIn a short time from now; soon.
“Boarding will begin shortly at gate twelve.”
2adverbeventA short time after or before another event.
“She arrived shortly after the speeches had started.”
3adverbcurtIn a curt, sharp way.
“'That is not your business,' he said shortly.”
Too few real examples of this word to estimate which sense is commonest.
Shortly is short with -ly on the end, and it has been that from the beginning: Old English sċortlīċe already meant shortly, before long, soon, and Middle English carried it on as schortly. The picture is a short stretch of time between now and the thing you are waiting for.
Old English
sċortlīċe — shortly; before long; soon
Middle English
schortly
English, today
shortly
From Middle English schortly, schortliche, from Old English sċortlīċe (“shortly; before long; soon”), equivalent to short + -ly.
Etymology from Wiktionary, CC BY-SA