coextend

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive & transitive verb To extend or cause to extend through the same space or duration.

from The Century Dictionary.

• To extend equally; cause to extend through the same space or duration; place so as to coincide or occupy the same extent or space.
• To reach to or attain the same place, time, or duration: used with with.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To extend through the same space or time with another; to extend to the same degree.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb transitive, intransitive To extend along with another.