You'll also see that the same word sometimes contains different (yet interconnected) meanings, depending on how it's used.
These words occur commonly in prayer and Tehillim (Psalms), and it helps to know what you're really saying when you use them.
Note: All the definitions come from Malbim. The definitions of torah, mitzvah, edut, & pikud come from Malbim on Tehillim 119:1.
Din, Dinim — דין , דינים
It's basically the judicial proceedings.
In connection to that idea, din often means "consequences," whether positive or negative.
We often speak of harsh din or sweetened din—meaning that the claims, accusations, and consequences end up harsh or sweetened.
Mishpat, Mishpatim — משפט , משפטים
In other words, mishpat is the verdict. (Or, in the case of its verb shafat, the act of reaching the verdict.)
Its root is shafat--שפט—often translated as "judged."
Shofet--שופט—is "a judge."
Mishpat also means the person-to-person (bein adam l'chavero) laws.
The reasoning behind a mishpat is understandable to the human mind (as opposed to chok, a law in which its reason is not comprehensible).
This is why, in Tehillim for example, different kinds of mishpatim are mentioned.
There is mishpat b'tzedek (laws & verdicts conducted with fair justice), like the mishpat of Hashem.
Then there is mishpat formed according to the social mores of a particular culture—and these mishpatim aren't always just.
Tzedek — צדק
It oversees the mishpat, the verdict, so that the mishpat concludes in justice and not corruption.
Torah, Torot — תורה , תורות
But it's also used to mean "law" or "commandment," especially in its plural form, torot.
When used colloquially, torah includes all the teachings of Hashem: beliefs, instructions, character traits, and all the behaviors applicable to a person.
Mitzvah, Mitzvot — מצוה , מצוות
Chok/Chukim — חוק , חקים
Edut — עדות
In particular, edut means the events of Beresheit: the Creation of the Universe & its continuing functions (like how the Sun always rises in the East & sets in the West, the Moon always remains in more or less the same place relative to the Earth & with predictable phases, the Earth spins at a consistent speed on its tilted axis, etc.)
This infuses renewed conviction into the verse edut Hashem ne'emanah—the edut of Hashem is faithful; the functions of the Universe remain stable & reliable (Tehillim 19:8).
Pikud, Pikudim — פיקוד, פיקודים
(Please see its root below--pakad—and note how they go together to embrace the full meaning.)
Zachar — זכר
It also implies a meaningful act—meaning, there's a purpose to remembering; it needs to be remembered.
Pakad — פקד
It includes the action of actually doing what was remembered—like when Hashem pakad et Sara: He not only remembered what He promised her, but also fulfilled it.
It also means "commemorate," which is an act of remembering—again, "commemorate" follows on the heels of "remembering;" it acts on what was remembered.
(Please see above for how it relates to pikud.)