These ROOT-WORDS are CLUD & CLUS meaning SHUT. It comes from the Latin claudo & clauses. The double spelling in English follows, as you see, the double spelling in Lation. CLUD & CLUS mean nothing by themselves. With the Prefixes and Suffixes added to them, however, they are meaningful and useful.
1. Recluse : re CLUSE (rek’ luse) n.
One who shuts himself away from others; as, a hermit
2. Conclusion : con CLUS ion (kon klue; zhun) n.
The end; as, the conclusion of the course
3. Conclusive : con CLUS ive (kon klue’ siv) adj.
Final; as, a conclusive statement
4. Exclude : ex CLUD e (Eks klude’) v.
To shut out; as, exclude from a club
5. Exclusion : ex CLUS ion (eks klue’ zhun) n.
The act of shutting out; as, he resented his exclusion
6. Exclusive : ex CLUS ion (eks klue’ zhun) n.
Tending to keep others out; as, exclusive power
7. Include : in CLUD e (in klude’) v.
To take in; to count; as, include in the group
8. Inclusion : in CLUS ion (in klue’ zhun) n.
The act of taking in; as inclusion of algebra in the program
9. Inclusive : in CLUS ive (in klue’ siv) adj.
Counting everything in
10. Preclude : pre CLUD e (pre klude’) v.
To close beforehand; to hinder11. Preclusion : pre CLUS ion (pre klue’ zhun) n.
State of hindering; preventing
12. Conclude : con CLUD e (kon klude’) v.
To close; as, to conclude a trial
13. Reclusive : re CLUS ive (re klue’ sive) adj.
Favoring retirement from society
14. Seclude : se CLUD e (se klude’) v.
To shut away; to confine; as, seclude oneself in the woods
15. Seclusion : se CLUS ion (se klue’ zhun) n.
The act of shutting oneself up; as, Emily Dick inson lived inseclusion
16. Occlude : oc CLUD e (o klude’) v.
To shut the way; to bar a passage, as, the occlude light
17. Occlusion : oc CLUS ion (o klue’ zhun) n.
The shutting up; as, the occlusion of an opening
18. Occlusal : oc CLUS al (o klue’ zal) adj.
Relating to the surface of the tooth used in biting or grinding