A collision is usually taken to mean a physical impact: two cars which crash into each other would be a collision.
A conflict is normally between two or more things which disagree in some way, although its meaning can be extended across both tangible and intangible notions. For instance, you can have a conflict of opinions, where someone disagrees with the other, but you can also have a physical conflict (a fight, or a war).
Conflict, used in its physical sense, could be synonymous with collision.
In your case, you should say a Primary Key (PK) Conflict, as — and I'm assuming it's a duplicate here — the primary keys disagree with each other because they are the same.
They don't physically bump into each other.
Lexical categories
One major difference is that despair is a noun or a verb and that hopeless is an adjective.
For instance, you could say
"The situation is hopeless".
By which you would mean that there is no hope that the situation could improve.
And for despair you could say:
"He died in despair"
Here "despair" is a noun. Or
"I shall despair of ever seeing my
native country again".
Here instead it is a verb.
Comparing them for good
If you want to compare them as nouns, then you should compare "despair" to "hopelessness".
Strength
Although I'm not a native English speaker, I'd say that despair is stronger. "despair" is slightly more emotionally charged. You have a "feeling of hopelessness" but you "cry in despair".
Origin
As so often in English when you have two different words for a common thing one is from Saxon origin and the other is from Norman origin. And as usual rather than replacing one by the other, usage has given them complementary meanings.
So your question is definitely a valid one: there are shades of meaning.
"Hope" is a word from Saxon origin (compare to German "Ich hoffe dass...", I hope that...). "hopeless" => "hoff[nungs]los"
"Despair" is from Old French "despoir" (nowadays in modern French "désespoir" (noun) or "désespérer" (verb)).
Other examples
As an opening to other similar cases also consider the following list
- "Ask", English and "demand"
(stronger), from French.
- "Bit" and "morsel" both coming from the idea of biting (mordre) but the former more general than the latter.
- "Wish" and "desire" (stronger).
- "Might" and "power".
- "Room" and "chamber".
- "Answer" and "respond".
- "Begin" and "commence".
Taken from the second episode of The Adventure of English.
Best Answer
Segments
Some objects are naturally segmented, they have marks or narrowings between segments. These are places where the object can be easily and naturally separated. The segments are usually all alike in form. Think of an orange.
Parts
Some objects are compound objects that consist of an assembly of smaller dissimilar objects. We can separate these compound objects these into their constituent parts. Think of an internal combustion engine.
Pieces
Some objects don't have obvious segments but can still be divided into pieces at arbitrary points. The pieces need not be even in size and there is an undertone of destructive or irreversible breaking. Think of a (stereotypical circular uniform) cake.
Fragments
Some objects, when subjected to some sufficiently violent force, can shatter into multiple fragments of mostly random size and shape. If the other fragments are lost, you may find only one fragment and have no other knowledge of the form of the whole object. Think of a dropped Ming vase.
Sections
Some objects are designed to be cut apart or are commonly cut apart. The word section is derived from the Latin word for cutting and may be appropriate for a deliberate and careful cutting of some extract from a larger source. There is, to me, an implication that the cutting points are not accidental. Think of plumbing pipes
English text
Written English language text is usually written in sentences, paragraphs and perhaps chapters. These form obvious segmentation points, so when your extract is made at a balanced pair of such boundaries, the term segment is more appropriate. However, why not just use sentence or paragraph as appropriate?
If you spilled ink onto a page of text, it might be better to say that a part of the text was obscured - since (unless by unlikely coincidence) the obscured part is not an exact sentence or paragraph.
If a page of text is burnt or torn and scattered, you might consider any remainder to be a fragment.
As HorusKul commented, since successive English sentences are not often very similar, they are not very much like segments and the word section is more likely to be appropriate.
Updated to clarify segments, pieces, parts and sections. Updated: fragments.