This astronomical word has always fascinated me, not so much for its meaning as its consonants and repetition. My handwriting includes flamboyant loops and this word is a joy to write, you get to loop the loop five times (my ‘z’s have loops too…)
OED defines it, among other meanings, as ‘both conjunction and opposition of two heavenly bodies, or either of the points at which these take place, esp. in the case of the moon with the sun (new and full moon).
A loopy word, all in all.