specus

Etymology
Usually viewed as a derivative of, although De Vaan is doubtful of this etymology.

Noun

 * 1) cave, grotto
 * 2) ditch, canal, drain
 * 3)  pit
 * 4) chasm, abyss
 * 5)  cavity
 * 1)  pit
 * 2) chasm, abyss
 * 3)  cavity
 * 1)  cavity

Usage notes
While this word can be used in all three genders, as illustrated above, the masculine is by far the most common. The feminine was used ante-classically and in the Silver Age of Latin, with its archaising tendencies; the neuter (which then includes specum) is mostly poetic.