the.com/opener

means A person or thing that starts something off — most often the opening act, item, or move in a sequence.

from A straightforward agent noun: 'open' plus the suffix '-er,' which turns verbs into 'the one who does it' (as in baker, singer). English has stacked '-er' onto 'open' since the word has existed as a verb; the specific sense of 'opener' as a bottle-opener or an opening act or line is just that same old machinery applied to newer jobs — the thing or person that does the opening.