R to LaTeX – use xtable to produce long table with line wrapping

I have a table with a large number of rows (90) and each contains a name, a definition, plus another text column. I am trying to output to latex such that this spans multiple pages and also fits to page width.

library("xtable")
glossary2<-data.frame(names=letters[1:4],definition=c("very long long long text","very long long long long long text","very long long long long long long text","very long long long text"),include=c(NA,"YES",NA,"NO"))
glossaryprint<-xtable(glossary2,label="tab:codebook",caption="glossary")

Further to the xtable documentation I have been able to produce the following

To make it fit to page width:

align(glossaryprint)<-"lXXX"
print(glossaryprint,tabular.environment="tabularx",width="\\textwidth")

To make it fit over multiple pages:

print(glossaryprint,tabular.environment="longtable",floating=FALSE)

However, combining the two techniques is causing me difficulties. I think I may have to have split the table into tables of say 20 rows each and use tabularx but that's very clunky and a lot of repeating code.

Is anyone able to suggest a method for making one long table fit to page width and linewrap inside columns when outputting to Latex using R functions?