Because I'm pretty good at distracting myself, I got caught up recently in re-formatting one of my really old books (long story). While erasing unnecessary line breaks, I couldn't help but notice one word appearing again and again...and again and again. It was everywhere, and it was being used the wrong way 50 percent of the time. That word stuck out at me, and I started thinking about how often I've been seeing it in recent months. That's when I realized that it may just be the most over-used descriptor in fiction. This was quickly followed by the revelation that I can never, ever use it again...and I don't think you should, either. Allow me to plead my argument against the word slightly.
Insert Your Adverb Here
She smiled slightly. "I didn't expect to see you here."
He nudged her arm slightly. "Did you see that?"
I felt the room shake, slightly, as the big truck roared past.
I'm getting slightly tired of all this.
The examples above are pretty good approximations of recent sentences I've read in fiction containing the word slightly. And honestly, they're all pretty poorly written because of that word. Slightly isn't just an over-used descriptor...it's also a bad one.
By definition, slight means small, or some derivative thereof -- when it's used as an adjective. As a verb, slight means to treat something or someone as if they are small. For example: "The movie star was slighted by the Academy Awards when she wasn't nominated."
When you add ly, slight becomes the adverb slightly...also known as the one-size-fits-all word for any writer in a describing jam. Add slightly to any sentence, suddenly it feels a little bit fancier. Why shrug when you can shrug slightly? Why chuckle when you can slightly chuckle? Why come up with a better word, when this one can be shoved anywhere?
Because it sounds fairly horrible, that's why. Let's take the prose and put it into a real world context. What does a slight smile look like? What does a slight laugh sound like? To what degree of pain does one feel a slight nibble or a slight kick, and what would I hear if you let out a slight sigh?
Slightly isn't a degree, and it's isn't at all a good word. My idea of slightly might be totally different from yours, and as an author you've got to be more specific than that so I know what you're actually trying to convey. Slightly is just too vague, and it's too easy.
Thankfully, you get to the use the entire rest of the English language to write your descriptive text. That gives you over a million different words to choose from, and I'm going to start you off with a dozen that are perfectly serviceable synonyms for slightly: gently, weakly, ineffectually, somewhat, hardly, imperceptibly, daintily, casually, lightly, marginally, scarcely and faintly. Now, go write!