The Compendium of the Social Doctrine of the Church gives this definition of solidarity:

Solidarity is also an authentic moral virtue, not a “feeling of vague compassion or shallow distress at the misfortunes of so many people, both near and far. On the contrary, it is a firm and persevering determination to commit oneself to the common good. That is to say to the good of all and of each individual, because we are all really responsible for all”[418]. Solidarity rises to the rank of fundamental social virtue since it places itself in the sphere of justice. It is a virtue directed par excellence to the common good, and is found in “a commitment to the good of one's neighbour with the readiness, in the Gospel sense, to ‘lose oneself' for the sake of the other instead of exploiting him, and to ‘serve him' instead of oppressing him for one's own advantage (cf. Mt 10:40-42, 20:25; Mk 10:42-45; Lk 22:25-27)”[419].

(via Insight Scoop)

Is solidarity, then, identical to legal or general justice? Or is it a virtue allied to legal justice, akin to the virtue of perseverance or endurance (a kind of fortitude)? From the text it does not seem that different from legal justice. Is it distinguished within the Compendium from (the virtue of) social justice?