The saying, 'Every day is a school day' couldn't be more true when it comes to the vast and complex English language.

With approximately 170,000 words currently in use and an additional 47,000 considered obsolete, according to the Oxford English Dictionary, it's no wonder we're always learning something new.

Laurie Knox, a linguistics expert, frequently shares his knowledge on TikTok, delving into the fascinating world of words and enlightening his followers on various aspects of the English language.

In his latest video, he shed light on seven common words that are actually acronyms, which might surprise many.

An acronym is a shortened form created from the initial letters of other words, pronounced as a single word, such as ASAP (as soon as possible) and NASA (National Aeronautics and Space Administration).

1. Captcha 

Often encountered when verifying your identity on websites to prevent bot access, Laurie explained: "It stands for 'Completely Automated Public Turing test to tell Computers and Humans Apart'."

2. E-fit 

Commonly used in law enforcement to create electronic facial images to identify suspects, Laurie revealed it actually stands for 'Electronic Facial Identification Technique'.

3. Taser

Another tool in the police arsenal is the taser. "Did you know this is an acronym too?" Laurie queried. "It stands for 'Tom A Swift Electronic Rifle'." The name originates from Victor Appleton's Tom Swift series of books from the early 1900s, one of which was titled, Tom Swift and His Electric Rifle.

4. BASE jumping

Fourth on the list is BASE jumping, an extreme sport that involves leaping from fixed structures - often a building or a bridge. According to Laurie, the full name of this unusual hobby is 'Buildings Antennas Spans Earth' Jumping.

5. Scuba diving

Next is a much more common activity - scuba diving, an underwater practice using breathing aid. "This stands for 'Self Contained Underwater Breathing Apparatus'," Laurie explained.

6. Laser

An everyday word - but one you're likely not to have realised is an acronym - is laser, a device that emits a beam of coherent monochromatic light. "It stands for 'Light Amplification by Stimulated Emission of Radiation'," Laurie added.

7. Gulag

Laurie concluded by revealing that he'd only recently learned that gulag is actually a Russian acronym used in English - referring to a system of labour camps maintained in the Soviet Union between 1930 and 1955. "It essentially means 'Chief Administration of Corrective Labour Camps' [in translation]," Laurie stated. However, in its native language, it stands for 'Glavnoe Upravlenie ispravitel'no-trudovykh LAGerei'.

"Every day is a school day, love these," remarked one impressed TikTok user, clearly appreciative of the content. "Brilliant!" concurred another. "Learned something new again!"

A third shared: "I already knew about scuba and laser, I should've known about taser." Meanwhile, a fourth commentator added their own trivia to the mix, saying: "TWAIN is one I like, 'Technology Without An Interesting Name'.