These ROOT-WORDS are FEDER, FIDE, FID & FEAL which come from the Latin fidere which means TRUST & have FAITH. The various spellings are interesting, and due, no doubt, to the various languages in which these ROOT-WORDS are used. No. 12 when used for the feminine is spelled with an e - confidante (French).
1. Federacy : FEDER acy (fed’ er a si) n.
An alliance or confederacy
2. Federal : FEDER al (fed’ e ral) adj.
In the nature of an alliance; united
3. Federation : FEDER action (fed e ray’ shun) n.
A union; alliance through agreement
4. Federalism : FEDER alism (fed’ e ra liz um) n.
The principle of national organization
5. Federalist : FEDER alist (fed’ e ra list) n.
One who believes in federalism
6. Federate : FEDER ate (fed’ e rate) v.
To unite in mutual loyalty and faith
7. Confederacy : con FEDER acy (kon fed’ e ra see) n.
A union for mutual support and common action
8. Confederate : con FEDER ate (kon fed’ e rat) n.
One of a band united for a purpose; an accomplice
9. Bona fide : bona FIDE (boe’ na fide) adj.
In good faith; genuine
10. Confide : con FIDE (kon fide’) v.
To have trust in someone; as, to confide in a friend
11. Confident : con FID ent (kon’ fid ent) adj.
Self-reliant
12. Confidant : con FID ant (kon’ fid ant) n.
The person in whom one can confide
13. Confidence : con FID ence (kon’ fid ens) n.
Self-reliance
14. Confidential : con FID entail (kon fi den’ chal) adj.
In the nature of a secret; as, confidential information
15. Fealty : FEAL ty (fee’ al tee) n.
Loyalty; fidelity to duty
16. Fidelity : FID elity (fi del’ it ee) n.
Faithfulness; fealty
17. Infidel : in FID el (in’ fid el) n.
One who has no faith
18. Infidelity : in FID elity (in fi del’ it ee) n.
Faithlessness; disloyalty
19. Perfidy : per FID y (per’ fid ee) n.
Disloyalty; treachery; deceit
20. Perfidious : per FID ious (per fid’ ee us) adj.