Important means anything that is valuable or substantial, other words that convey the same meaning would be crucial, critical, imperative, urgent, essential, etc... Antonyms would be non-essential, meaningless, trivial and optional.
uninteresting
Cooliousis
high up!!!
You might be able to use words like 'left', or 'departed'.
However, instead, on the other hand, except, besides, nonetheless, otherwise, although, despite the fact, meanwhile & although
you are not
two
rather, preferably, alternately
since
execute
uninteresting
Abscond.
Cooliousis
Special?
high up!!!
Thou, ye, thee
Artillery,Armory