mid-

Usage Note: Many compounds other than those entered here may be formed with mid-. In forming compounds, mid- is normally joined to the following word or element without a space or hyphen: midpoint. However, if the second element begins with a capital letter, it is always separated with a hyphen: mid-May. It is always acceptable to separate the elements with a hyphen to prevent possible confusion with another form, as, for example, to distinguish mid-den (the middle of a den) from the word midden. Note that the adjective mid¹ is a separate word, though, as is the case with any adjective, it may be joined to another word with a hyphen when used as a unit modifier: in the mid Pacific but a mid-Pacific island.