Speaking of Hebrew, my Hebrew grammar book states that
In numbering days of the month and years, the cardinals are very frequently used instead of the ordinals even for the numbers from 1 to 10…
which explains “תשעה באב” (tishah b’Av), [day] nine in Av.
What I was wondering about is why it’s בְּ there while “בְּתִשְׁעָה לַחֹדֶשׁ” (on the ninth day of the month) uses לְ, here meaning [belonging] to ? The section on prepositions simply translates
בְּ [poet. בְּמוֹ] in, at, with.
לְ [poet. לְמוֹ] towards, (belonging) to, for, Lat. ad.