One might note that “secular” and “humanism” as terms in English and their Latin roots in Medieval usage, did not mean “atheistic” or “non-religious.” “Secular” meant in Latin usage to refer to the “world” – meaning not the monastery. A secular priest would be a priest who was not cloistered. Erasmus was a “humanist”—but today a look at some online dictionaries suggests that “secular” in English is coming to mean “non-religious” or “non-spiritual.”
EIN suggests that one try to avoid getting entangled in “merely” verbal definitions and focus on what is substantial. If by “spiritual” one includes cultivating a life of reverence for others and values, an openness to that which seems worthy of one’s loyalty and love… then being “sacred” can include “being spiritual.” There are many points where a so-called secular ethicist and (for example) a Christian ethicist might agree whole-heartedly.
One contrast that is worth recording, however, consists in taking on values in terms of “the big picture.” Many of those who identify themselves as secular humanists are atheists in the tradition of naturalism and many (but not all) tend toward some version of physicalism. Debate on the role of a person taking into account “the big picture” is sometimes played out by a secular humanist (such as Philip Kitcher) who sees the value and meaning of life in terms that are immediate or immanent and that these values are not diminished in light of, say, the presumed likely annihilation of each individual at death or the loss of all life in our cosmos. For a discussion of such concerns, see the revised entry “Afterlife” in the Stanford Encyclopedia of Philosophy.
For an interesting, sensitive calling for theists and atheists, believers and skeptics, to recognize common ground is Ronald Dworkin’s Religion without God.