Learn Turkish: İçindeki korku tamamen yüzüne aksetti. - The fear inside him completely reflected on his face.

This is exactly what this lesson is about! The word comes from the noun akis (reflection) and the auxiliary verb etmek (to do). When combined, the second vowel of akis drops out (vowel elision), leaving aks. Whenever a noun undergoes a sound change like vowel dropping or consonant doubling when paired with an auxiliary verb, the two words are written together as one: aksetmek. Finally, the past tense suffix -di changes to -ti to match the voiceless s.

Why is it yüzüne (to his face) instead of yüzünde (on his face)?

In English, we say something reflects 'on' a face, which might tempt you to use the locative case (yüzünde). However, in Turkish, the verb aksetmek (to reflect) takes the dative case (-e/-a) because the reflection is seen as projecting or moving 'onto' a surface as a destination.

How exactly do the suffixes in içindeki build the meaning 'the fear inside him'?

Let's break it down: iç (inside) + -i (his, 3rd person possessive) + -n- (buffer letter) + -de (locative case) + -ki (relative suffix: 'the one that is'). Literally, it translates to 'the one that is in his inside'. The -ki acts like an adjective maker, linking the location directly to the noun korku.