1. A very high mountain. Specifically, in the plural, the highest chain of mountains in Europe, containing the lofty mountains of Switzerland, etc. Nor breath of vernal air from snowy alp. (Milton) Hills peep o'er hills, and alps on alps arise. (Pope)
2. Something lofty, or massive, or very hard to be surmounted.
The plural form alps is sometimes used as a singular. The alps doth spit.
Origin: L. Alpes the alps, said to be of Celtic origin; cf. Gael. Alp a high mountain, ir. Ailp any huge mass or lump: cf. F. Alpes.