This is the 5390th most frequent Turkish word.
korkusu
"Fear of" or "phobia of."
'korkusu' is used as the genitive case of a noun phrase indicating someone's fear, specifically, 'the fear of being alone'.
O, yalnız kalma korkusu yaşardı.
He used to experience the fear of being alone.
'korkusu' here exemplifies a specific fear tied to an event or circumstance, in this case, falling from a height.
Yüksekten düşme korkusu nedeniyle köprüden geçemedi.
He couldn't cross the bridge due to the fear of falling from a height.
'korkusu' is employed to express a general fear experienced during childhood, namely, 'a fear of the dark'.