Install LibreOffice-Writer Only not LibreOffice whole package

Yes! sudo apt install libreoffice-writer will install that package as well as certain other core LibreOffice packages. You will need to install the help package separately if you want help offline.

See the following output:

$ apt list --installed | grep -i libreoffice

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

libreoffice-base-core/bionic,now 1:6.2.2-0ubuntu0.18.04.1~lo1 amd64 [installed,automatic]
libreoffice-calc/bionic,now 1:6.2.2-0ubuntu0.18.04.1~lo1 amd64 [installed]
libreoffice-common/bionic,bionic,now 1:6.2.2-0ubuntu0.18.04.1~lo1 all [installed,automatic]
libreoffice-core/bionic,now 1:6.2.2-0ubuntu0.18.04.1~lo1 amd64 [installed,automatic]
libreoffice-gtk3/bionic,now 1:6.2.2-0ubuntu0.18.04.1~lo1 amd64 [installed]
libreoffice-help-en-us/bionic,bionic,now 1:6.2.2-0ubuntu0.18.04.1~lo1 all [installed]
libreoffice-math/bionic,now 1:6.2.2-0ubuntu0.18.04.1~lo1 amd64 [installed,automatic]
libreoffice-style-breeze/bionic,bionic,now 1:6.2.2-0ubuntu0.18.04.1~lo1 all [installed,automatic]
libreoffice-style-colibre/bionic,bionic,now 1:6.2.2-0ubuntu0.18.04.1~lo1 all [installed,automatic]
libreoffice-style-tango/bionic,bionic,now 1:6.2.2-0ubuntu0.18.04.1~lo1 all [installed,automatic]
libreoffice-writer/bionic,now 1:6.2.2-0ubuntu0.18.04.1~lo1 amd64 [installed]
$ 

The ones listed as "installed" are what I installed. The rest listed as "installed,automatic" come in as a matter of course.

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You can do a "dry run" to see what would be installed using -s to specify you're only running a simulation and so sudo isn't needed.

With 19.04,

apt install -s libreoffice

gives me

0 upgraded, 83 newly installed, 0 to remove and 0 not upgraded.

Whereas

apt install -s libreoffice-writer

gives me

0 upgraded, 28 newly installed, 0 to remove and 0 not upgraded.

This command will install only LibreOffice Writer without any recommended packages:

sudo apt-get install --no-install-recommends libreoffice-writer libreoffice-gtk3