Borrowed (as a title) from bar; the heir (apparent to the throne) -- son.
see HEBREW bar
H1248. bar
I. בַּר noun masculine son (Aramaic בַּר, Syriac ) only in late Hebrew of Proverbs 31:2 (twice in verse) (both construct), 31:2 suffix בְּרִי; בר נשׁקו Psalm 2:12 kiss the son, ᵑ6 Modern Vrss Ges De Pe et al.; receive instruction ᵑ7; δράξασθε παιδείας ᵐ5; apprehendite disciplinam ᵑ9 Ew; kiss purely, do sincere homage Aq Symm Jerome BrMP 136; emendation Lag (מוֺסָרוֺׅ מוֺסֵרוֺ נַשְּׁקוּ put on his bonds (compare 2:3) so Kmp CheOP 351.