I was experimenting with Google's ngram tool, and came upon this curious result:
My assumption would have been with the more open attitudes towards discussion of sex, usage for "erection" would have gone up. Yet it has gone down by over a factor of 3 since 1876. Searching some old period bands (such as 1820-1840), I saw that the primary use for "erection" had been in the context of erecting a building. However, the current biological meaning existed as well.
My guess is that people are using the building-related "erection" a lot less, to avoid unintended sexual connotations. If so, they substitute some other terminology. Either that or we write a lot less, proportionately, about building than we used to.
I added "hard-on" to the graph, suspecting it was supplanting "erection", but as the graph shows, it is still relatively insignificant. (It began steady ascent around 1958.) I cannot think of another word likely to be used in books that would be supplanting the biological meaning.
BTW, while writing this, I graphed the same ngram, but terminated it at 2016. The slight upward slope has continued steadily since about 1996. It had yet to reach .00040%, though. This may be illustrating what I expected initially, more open attitudes toward sex.