maintain
/mān-ˈtān/
verb
to keep in an existing state (as of repair, efficiency, or validity) : preserve from failure or decline
to sustain against opposition or danger : uphold and defend
to continue or persevere in : carry on, keep up
maintain machinery
idiom
to make it possible for life to exist or continue
They barely had enough food to maintain life.
idiom
to not become angry or upset
He was struggling to maintain his cool/composure.