This is the 708th most frequent Spanish word.
miedo
Fear.
In this sentence, 'miedo' means 'fear', and it is used to express the feeling of fear that the subject has towards something, in this case, heights.
Tengo miedo a las alturas.
I am afraid of heights.
Here, 'miedo' defines a triggered emotion of fear in response to a specific event, the loud thunder.
El niño lloró de miedo cuando escuchó el trueno.
The child cried with fear when he heard the thunder.
In this sentence, 'miedo' is discussed as a general concept of fear, particularly focusing on the fear of the unfamiliar or unknown.