I’d never really thought about the oddness of the term deed poll, ‘British: a deed (as to change one’s name) made and executed by only one party,’ until a Wordorigins contributor brought it up. Dave Wilton‘s answer provides one of those surprising and enjoyable bits of linguistic history that got me interested in linguistics in the first place:
Poll originally meant head, and is commonly used in reference to the counting of heads. It’s either from or cognate with the Dutch pol meaning top or summit.
In the case of deed poll, it comes from the verb meaning to shave (the head). Since this type of change to a deed affects only one party—unlike a transfer of ownership—the document edges would be cut straight. For two-party documents, the cut would be jagged so the two halves could be matched. Deed poll dates to the 16th century and is contrasted with deed indented.
So deed poll has the same structure as battle royal or linguist manqué. Who knew?