Learner's definition of OPENER
1 : a tool, device, or machine that is used to open something
a bottle opener
a garage door opener
2 : the first game, performance, etc., in a series
This game will be the season opener [=the first game of the season] for both teams.
The album's opener is a slow love song.
the meal's delicious opener [=starter]
: as the first thing to be thought about or said : to begin with
She began by asking what we'd done with her money. And that was just for openers!
(chiefly US) “What didn't you like about my poem?” “Well, for openers [=for starters], I hated the title.”