"pseudo-", "quasi-" "semi-" and

Question

I was wondering about the meaning of "pseudo-", "quasi-" "semi-" and possibly other related prefixes, in general cases.

Particularly, in engineering and science, there are quite a few terms named with these prefixes. For example, "quasi-integrable", "pseudo-Newton method", "semigroup". But I never get to understand their differences in usage.

Just to add some color to the conversation... a hemidemisemiquaver is a 1/64 note. — oosterwal, Apr 05 '11 at 14:30
Musicians who lack rhythm and timing play their 1/64 notes as pseudoquasisemiquavers. — oosterwal, Apr 05 '11 at 19:48
Which prefix is preferred if one object has some of the defining characteristics of another but may or may not have all or be of the same (a priori specified) class? For example, two polynomials may have the same number of roots and in the same location but not be equal functions. — user02138, Jul 16 '11 at 22:34
There is also the "-oid" suffix used in a similar way, e.g. "asteroid" = "like a star", "cuboid" = "like a cube", etc. — Dai, May 02 '22 at 07:05

score 44 · Accepted Answer · answered Apr 05 '11 at 01:15

Pseudo- comes from the Greek for false/lie and refers particularly to something not genuine.

Quasi- comes from the Latin for almost and refers to something that is almost something else.

Semi- is the Latin for half and refers to something that is half-something else

In late usage, however, all three have been used to mean sort-of-

Mitch · Answer 2 · 2011-04-05T01:55:56.783

12

As others have said, pseudo = false, quasi = almost, semi = half.

In engineering and science, these tend to have fairly technical meanings. That is, a pseudopod is something that looks like a foot but is not, semiannually means twice a year (and I can't really think of an accepted repeatable term that begins with 'quasi').

In mathematics, however, all bets are off. A semigroup is like a group and has fewer defining properties than a group, but in no way is it anything like half of a group. Similarly a quasigroup. (this is a general notice about mathematical terminology, the inventors of the terminology usually have some metaphor in mind when the technical term is chosen, but that metaphor hardly ever translates to anything meaningful).

edited Apr 05 '11 at 01:55

answered Apr 05 '11 at 01:26

Mitch

71,423

E.g., quasi-scientific? – msanford Apr 05 '11 at 01:53
3

Quasar: Quasi-stellar radio source (quasi-stellar, because it seems like a star, but is infact a galactic nucleus) – Dancrumb Apr 05 '11 at 01:59
@msanford: or quasi-governmental? I looked them up and none of the words starting with 'quasi-' sound 'official' to me. They all sound like neologisms or nonce words. – Mitch Apr 05 '11 at 02:07
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@Mitch, so, all you've found are quasi-words? ;) – msanford Apr 05 '11 at 02:11
1

And pseudocode is stuff that looks like code but isn't. – Jon Purdy Apr 05 '11 at 07:10
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@Mitch: my favourite being: Quango - quasi-autonomous non-governmental organisation. Not so much a nonce word, more a nonsense word. – Matt E. Эллен Apr 05 '11 at 08:28
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Actually quasicode is a closer description for pseudocode than pseudocode. – SWeko Apr 05 '11 at 10:25
+1 for the sheer value of the note on mathematics. 'notice about mathematical terminology / inventors have some metaphor in mind / metaphor hardly ever translates to anything meaningful'. (Should be repeated at the start of 'semieach' (yikes) math class. Especially in universities.) – n611x007 Apr 26 '13 at 05:06
Quasistatic is a standard engineering term. – Evgeni Sergeev May 15 '17 at 14:05

score 7 · Answer 3 · answered Apr 05 '11 at 01:14

7

Quasi - almost
Pseudo - fake or impersonating
Semi - half

answered Apr 05 '11 at 01:14

Sam

5,430

score 2 · Answer 4 · answered Apr 05 '11 at 08:09

In civil engineering the term quasi-permanent is used for actions (loadings). It has more the meaning of equivalent that almost.

In very simple words, we suppose that the action is permanent although it's true nature is quite different. This in practice means that we load the structure with the equivalent of a permanent load.

What permanent means in civil-engineering context is another question!

"pseudo-", "quasi-" "semi-" and

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