This is the 10820th most frequent French word.
obscures
Dark, dim, or unclear.
In this sentence, 'obscures' is used as an adjective describing the physical darkness or dimness of the alleys.
Les ruelles de la vieille ville sont obscures la nuit.
The alleys of the old town are dark at night.
'Obscures' here metaphorically conveys a lack of clarity or understanding regarding someone's motivations.
Ses motivations restent obscures pour nous.
Their motivations remain unclear to us.
In this instance, 'obscures' is employed figuratively to denote negativity or a menacing nature in his thoughts.