/kɪˈlɒmɪtər, ˈkɪləˌmi‐/ Show Spelled[ki-lom-i-ter, kil-uh-mee‐]
a unit of length, the common measure of distances equal to 1000 meters, and equivalent to 3280.8 feet or 0.621 mile. Abbreviation: km
Also, especially British , kil·o·me·tre.
1800–10; < French kilomètre. See kilo-, meter(1)
kil·o·met·ric /ˌkɪləˈmɛtrɪk/ Show Spelled[kil-uh-me-trik] kil·o·met·ri·cal, adjective
The usual pronunciation for units of measurement starting with kilo-, as kilocalorie, kiloliter, and kilohertz, as well as for units of length ending in the base word meter, as centimeter, hectometer, and millimeter, gives primary stress to the first syllable and secondary to the third. It would seem logical for kilometer to follow this pattern, and in fact the pronunciation /ˈkɪləˌmitər/ Show Spelled[kil-uh-mee-ter] has been used since the early 1800's. A second pronunciation: /kɪˈlɒmɪtər/[ki-lom-i-ter], with stress on the second syllable only, was first recorded in America before 1830. Although often criticized on the basis of analogy, this pronunciation has persisted in American English, increasing in frequency, and has gained popularity in British English as well. It is reinforced by words for instruments (rather than units) of measurement ending in -meter, as thermometer, barometer, and speedometer, having stress on the -om syllable. Both pronunciations are used by educated speakers, including members of the scientific community.
From the excellent dictionary.reference.com -.