An Etymological Dictionary of Astronomy and Astrophysics

1. A covering for the head.
   

2. The top part of something (such as a hill or mountain). → polar cap.
   

3. A removable cover or lid.

Etymology (EN): M.E. cappe; O.E. cæppe “hood, head-covering,” from L.L. cappa “a cape, hooded cloak,” possibly shortened from capitulare “headdress,” from L. caput “head;” cf. Pers. Lori kapu “head,” kapulek “skull, middle of the head;” Kurd. Kurmanji qaf “head;” Pashto kaparay “skull;” Farâhâni kapâl “a blow on the head.”

Etymology (PE): Kolâhak, diminutive of kolâh “cap;” maybe related to PIE base *kel- “conceal;” cf. L. celare “to hide, conceal,” occulere “to dissimulate;” Gk. kalyptein “to cover,” kalia “hut, nest;” Skt. cala “hut, house;” Goth. hilms “helmet,” huljan “cover over,” hulistr “covering;” E. hull “seed covering,”
from O.E. hulu, from O.H.G. hulla, hulsa; O.E. hol “cave;”