One who sings or leads singing in advance or at the beginning; possibly a choir leader or precentor who begins the song.
Fore- (before/leader) + singer (one who sings). Likely emerges from church music contexts where a 'foresinger' would begin the hymn for others to follow.
Medieval churches had strict hierarchies of singers, and 'foresinger' likely referred to the precentor—the person whose job was literally to sing first so others would follow, a role so important it had its own title, yet we've completely replaced it with generic 'choir director.'
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