That's because rapture is an English word.
"harpazo" is the Greek word for "rapture".
1 Thessalonians 4:17 Then we which are alive and remain shall be caught up HARPAZO/RAPTURE together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.
When this verse was translated into Latin from Greek, the Greek word "harpazo" was replaced by the the Latin verb "rapio" meaning "to catch up" or "take away" (the Latin noun "raptus" "a carrying off"). The Latin word “rapiemur” is the word St. Jerome used for “caught up” when he translated 1 Thess 4:17 in the Latin Vulgate Bible. In Middle French "rapiemur" is "rapture" meaning "to carry away" which is the same meaning as Rapture in English. So while the English word RAPTURE is not in scripture the Greek word HARPAZO is in scripture and it is the origin of the word rapture. So, yes, a rapture is very biblical. A pre-trib rapture is not biblical because Paul places the rapture after the tribulation and second coming and after the resurrection of the dead. The rapture then will come after the great tribulation known as "post-trib".