French translation of "fils majeur & fille majeure" #general

Roberta Solit

In a Paris, French marriage record >from the year 1909, the groom is described as
"fils majeur". The bride is also referred to as a "fille majeure". I understand
that this translates as a "major son" and a "major daughter".
Wondering if anyone else has seen this expression, and if so, what does it mean?
Single, only, oldest etc?
Thank you in advance,
Roberta Solit

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