Why is the ninth month called September?
mid-13c., avauncen, transitive, "improve (something), further the development of," from Old French avancier "move forward" (12c.), from Vulgar Latin *abanteare (source of Italian avanzare, Spanish avanzar), from Late Latin abante "from before," composed of ab- "from" (see ab-) + ante "before, in front of, against" (see ante).
The -d- was inserted 16c. on mistaken notion that initial a- was from Latin ad-. From c.1300 as "to promote;" intransitive sense is mid-14c., "move forward." Meaning "to give money before it is legally due" is first attested 1670s. Related: Advanced; advancing. The adjective (in advance warning, etc.) is recorded from 1843.
c.1300, "boasting, ostentation," from advance (v.). Early 15c. as "advancement in rank, wealth, etc." Advances "amorous overtures" is from 1706.