An alignment of astronomical objects whereby one object comes between the observer (or notional observer) and another object, thus obscuring the latter.
Especially, an alignment whereby a planetary object (for example, the Moon) comes between the Sun and another planetary object (for example, the Earth), resulting in a shadow being cast by the middle planetary object onto the other planetary object.
A seasonal state of plumage in some birds, notably ducks, adopted temporarily after the breeding season and characterised by a dull and scruffy appearance.
(Irish grammar) A mutation of the initial sound of a word by which voiceless sounds become voiced, voiced stops become nasal consonants, and vowels acquire a prothetic nasal consonant: see Appendix:Irish mutations#Eclipsis.