Declan comes from an Irish saint's name whose exact meaning has been lost to time, though it's popularly linked to ideas of goodness or virtue. Even without a settled etymology, centuries of association with a figure known for charitable work have given the name a steady moral undertone.
Not only Trines and Sextiles may be counted friendly aspects, but even Squares and Oppositions too, if there happen a Reception. - Cardan Girolamo (1501-1576)