noun
dry cough; hacking cough
A cough without phlegm, often persistent and irritating.
空咳が一週間も続いている。
I've had a dry cough for a whole week.
彼は空咳をして、喉の痛みを訴えた。
He gave a hacking cough and complained of a sore throat.
noun
intentional cough (to get attention)
A deliberate cough used as a signal, often to alert someone to your presence or to express disapproval.
部屋に入る前に、わざと空咳をして存在を知らせた。
Before entering the room, I gave an intentional cough to announce my presence.
Rarely used kanji form.
咳 is the general word for 'cough', while 空咳 specifically refers to a dry or intentional cough.
Compound of 空 (から, 'empty') + 咳 (せき, 'cough'), literally 'empty cough'.