Fiasco means a complete disaster or humiliating failure. Failure means lack of success. Both refer to something going wrong badly, hence they are synonyms.
Fickle means likely to change frequently, especially in loyalty or affection. Changing means not constant, shifting. Both describe inconsistency, which makes them synonyms.
Fiction means something invented or imagined, not real. Fabrication means something made up or false. Both refer to something unreal or invented, hence synonyms.
Fidelity means faithfulness or loyalty. Dedication means strong commitment or devotion. Both imply loyalty and devotion, making them synonyms.
Finicky means overly particular or fussy. Choosy means picky or selective. Both describe being very particular, so they are synonyms.
Flabbergasted means extremely surprised or shocked. Astonished means greatly surprised. Both convey strong surprise, which makes them synonyms.
Flimsy means weak, not strong or poorly built. Inadequate means not enough or insufficient. Both indicate weakness or lack of strength, hence synonyms.
Flounder means to struggle or act clumsily in difficulty. To struggle awkwardly has the same meaning. Both describe awkward struggling, making them synonyms.
Flurry means a sudden burst of activity or excitement. Commotion means noisy disturbance or agitation. Both involve sudden, busy, or noisy activity, so they are synonyms.
Folklore means the traditional beliefs, customs, and stories of a community. Traditional beliefs means long-held cultural ideas or practices. Both are about cultural traditions, hence synonyms.