surgical bandage for the stump of amputated limb; small iron skullcap
The imaginary line which represents the uppermost part of capital letters and some lowercase characters’ ascenders.
An imaginary line across the top of capital letters. The distance from the cap line to the baseline is the cap size. 
Roughly shaped crown and brim of felt or straw, to be blocked into hat shape.
An imaginary line drawn at the cap height.
Ca'pe·line` noun [ French, from Late Latin capella . See Chapel .] (Medicine) A hood- shaped bandage for the head, the shoulder, or the stump of an amputated limb. 
The capeline was a British woman's hat of the 18th century. The capeline had a wide, soft brim made from fine straw faced with silk and was tied with ribbons.
An imaginary horizontal line running across the tops of capital letters.