To extract a single element, you can use the [[ instead of [.
In your case:
newx <- c(0.5,1.5,2.5)
newy <- c(2,3,4)
out <- lm(newy ~ newx)
coefficients(out)[["newx"]]
[1] 1
You can also use the unname() function as follows:
unname(coefficients(out)[c("newx", "(Intercept)")])
[1] 1.0 1.5