negative, non-, bad, ugly, clumsy
—
不 centers on negation and reversal: it marks something as not, non-, or the opposite of good, leading to senses like bad, ugly, or clumsy.
unclear; obscure; indistinct; uncertain; ambiguous
un-; non-
anxiety; uneasiness; worry; apprehension; fear; insecurity; suspense
wonderful; marvelous; strange; incredible; amazing; curious; miraculous; mysterious
insufficiency; deficiency; shortage; lack; scarcity; deficit
impossible
dissatisfaction; discontent; displeasure; complaint; unhappiness
unnecessary; unneeded
injustice; unfairness; wrongdoing; iniquity; impropriety; irregularity; dishonesty; illegality; fraud
bad; poor; inferior; defective
bad(-tasting); unpalatable; unsavoury; unsavory; awful; terrible; unpleasant
unhappiness; sorrow; misfortune; disaster; accident
real estate
adultery; impropriety; (an) affair; immorality
impossible; incapable (of doing); unable (to do)
displeasure; discomfort; unpleasantness
wrong; bad; improper; unjustifiable; inadvisable
instability; insecurity; crankiness
disadvantage; handicap; unfavorable position
absence
unlawful; illegal
inconvenience; inexpediency; unhandiness
doubt; suspicion; question; strangeness
insufficient; inadequate; imperfect
不 is an ancient pictograph of a bird flying upward, later borrowed to express negation. The modern form is highly abstract and no longer resembles the original image.
The four simple strokes of 不 look like a barrier or a crossed-out sign, blocking or negating what comes before it. Think of it as a universal 'not' symbol.
For フ, imagine a big red 'F' stamp on a test paper, marking it as a failure: F -> フ, and the stamp says 'not good enough'.