Headwind is a wind that blows directly opposite of forward motion, or from the front. Headwind can also be used to describe anything that opposes growth or movement. It should always be spelled as one word, but can be singular or plural depending on context.
The antonym for headwind is tailwind, which blows from behind or directly in line with forward motion. It can describe anything that promotes growth or movement.
Examples
But trade will likely remain a headwind to U.S. economic growth in the second quarter partly because foreign imports outside of petroleum reached a record high in May. [Wall Street Journal]
The motor is there to ease the burden of pedalling, making it easier to go uphill or cycle into headwind, and it will help you cycle further, with less effort, than you could on a regular bicycle. [Eastbourne Herald]
Many stocks that have made big runs have sold off after earnings and input costs could be a headwind. [CNBC]