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I recently found out that “extrovert” is a misspelling and that it’s actually written extravert. That makes sense, because other words use the same prefix, e.g. extraordinary, extradite, etc., but nothing I can think of begins with extro-(1).

However, intro- and intra- seem to be two different prefixes. There is introduce and introspect on the one hand, and intravenous and the more recent neologism intranet on the other hand.

What is the difference between intro- and intra- and what are their origins?

((1) Even the end-credit section of a movie, the opposite of the intro, isn’t called an extro :) )

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Extrovert intro- intra- –  Andrew Leach May 25 '12 at 11:47
    
Hm, interesting. The close vote reasoning says “This question is too basic; it can be definitively and permanently answered by a single link to a standard internet reference source designed specifically to find that type of information.” — Such questions are explicitly welcome on StackOverflow. I wonder why English Language & Usage is different. –  Timwi May 25 '12 at 11:51
    
    
The more interesting question to me is: If intra is the opposite to extra, what is the opposite to intro? Or in different words: intra means inside, extra means outside, intro means into. So which word mean out? Outro? Why not extro? –  Em1 May 25 '12 at 12:22
    
Actually the couple of dictionaries I checked listed "extrovert" as the primary entry and "extravert" as an alternate spelling. The ever popular Google ngrams shows extrovert as far more common. books.google.com/ngrams/… –  Jay May 25 '12 at 15:41
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1 Answer 1

up vote 4 down vote accepted

The prefix extro- means ‘outwards’. The Oxford English Dictionary has entries for both extrovert and extravert, with no difference in meaning. The only other word in the OED beginning with extro- is ‘extrospective’. Its Latin origin is the preposition extra which means ‘outside’. The ‘o’ appears to have replaced the ‘a’ of ‘extra’ by analogy with the Latin adverb intro.

Intro itself means ‘inwards’, ‘to the inside’, and is used in that sense as a prefix in English verbs and adjectives. Intra is a Latin preposition meaning ‘inside’ and is the origin of the prefix in English adjectives, typically those found in biological contexts.

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Well, the examples of "intra-" words that come to my mind refer to things within some group or entity as oppopsed to between entities, like "intramural", "intradepartmental", "intragalactic", etc. –  Jay May 25 '12 at 15:38
    
@Jay: But there are also ‘intraacinous’, ‘intraamniotic’, ‘intrarticular’ and ‘intracardial’, to name but a few. –  Barrie England May 25 '12 at 17:56
    
Intra nos, this isn't a full answer. –  TimLymington May 25 '12 at 18:05
    
@TimLymington: I do me best, guv. –  Barrie England May 25 '12 at 18:08
    
@BarrieEngland I wasn't disputing that there are technical biological terms beginning "intra-". I was just trying to point out that your answer gave the impression -- intended or not -- that this prefix is primarily confined to such terms, when in fact there are at least a fair number of words used in more common speach. (As a percentage of total such words, the biological terms may be a large majority. If that's what you meant, no dispute.) –  Jay May 29 '12 at 14:49
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