The following examples are taken from OALD:
That section of the road is still closed.
The library has a large biology section.
the tail section of the plane
I wonder if I can substitute segment or part for these section without changing the intended meaning.
Section, segment, or part all have similar meanings, but the situations in which each can be used is different.
According to Oxford Dictionaries Online, a section is
- Any of the more or less distinct parts into which something is or may be divided or from which it is made up
- A distinct group within a larger body of people or things
Therefore, you only use section when the larger thing that the section is coming from can be, or is, divided into distinct parts.
According to Oxford Dictionaries Online, a segment is
- Each of the parts into which something is or may be divided
- Geometry A part of a figure cut off by a line or plane intersecting it, in particular
Thus, a segment is almost exactly the same as a section, and the two can be used interchangeably. However, segment carries a secondary meaning and so can also be used when specifically talking about lines and planes in geometry.
When you look up the word part in Oxford Dictionaries Online, you'll find that it has no less than 15 different meanings and submeanings. It is therefore the most broad and flexible of the three words we're studying, but it's general meaning is
An amount or section which, when combined with others, makes up the whole of something
So you can use part whenever you want to talk about any piece of a larger entity.
In terms of your examples...
"That segment/section of the road is still closed." Segment and section are interchangeable here. In my experience, section would be the most commonly used, but segment is equally valid, especially since a road is more or less a line, and in geometry we have line segments. You can also use part, but you lose the specificity you would have had with the other choices.
"The library has a large biology section." This is a special case. Section is the only acceptable word to use here. The biology section is a distinct part of the larger library. I have only ever heard people using section to reference specific areas of libraries, never segments, or even parts. And I've been in a lot of libraries.
"The tail section of the plane." Section is the most common word to use in this case. You can also say part, if you want to give a more informal tone.
I don't know if you meant for the question to be limited to just the examples you listed. Therefore, I'd like to point out a case where there is a difference in meaning between segment and section.
Earthworms are a type of segmented worm. Each little stripe on an earthworm is called a segment:
In contrast, a section (usually called a cross section) of a worm refers to any cut.
Section can also refer to any part of the animal, divided along its main axis. For example:
The worm’s anterior (front section) has the segments with the most specialised organs. The pharynx, behind the mouth, and the grinding gizzard together occupy about 10 segments. There is a thin oesophagus (the tube linking the throat to the stomach), and then the simple intestine begins at about the 15th to 20th segment, running to the terminal anus.
A part of an earthworm is an ambiguous term. It could refer to any portion, such as the front, or an organ such as a heart.
You can substitute in all your examples the word section with the word segment or part without any change in meaning.
Yet, when it comes to the sense of a representation of a solid object (such as in technical drawing) cut by an imaginary plan you can’t.
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