2 syllables:
blunder, bumper, bunker, clumber, cumber, dumper, dunker, hunger, jumper, junker, lumber, lumper, monger, number, plunder, plunker, slumber, stumper, sunder, thunder, tunker, umber, unbar, under, wonder, younger, younker

3 syllables:
brontosaur, sloganeer, hosteller, monitor, hollander, godmother, nodular, polymer, proposer, jocular, cockchafer, sodbuster, popular, cocklebur, modeler, hogchoker, goddaughter, commodore, colander, columnar, alcazar, oliver, blockbuster, pompadour, bolivar, gospeler, modeller, monomer, commissar, globular, onager, almoner, stomacher, gobbler, gossamer, commoner, nonpolar, conifer, nothosaur, gossiper, slopseller, asunder, back-number, bob under, box-number, boy wonder, call number, encumber, fall under, f number, go under, large number, like thunder, mach number, mass number, outnumber, page number, phone number, pole jumper, prime number, put under, real number, ski jumper, spelunker, stop number, tub-thumper, wave number, whole number

4 syllables:
biographer, atmometer, picometer, spectrometer, cryometer, psychrometer, tachometer, spherometer, manometer, astronomer, algometer, hodometer, unpopular, decametre, bilocular, demographer, photographer, pornographer, binocular, clinometer, bolometer, philosopher, kilometer, astrologer, speedometer, subocular, thermometer, geographer, reconciler, odometer, siphonophore, hygrometer, chronometer, micrometer, hydrometer, buckle under, complex number, compound number, disencumber, going under, index number, knuckle under, license number, magic number, newtown wonder, octane number, power hunger, po box number

5 syllables:
interlocutor, lexicographer, gas thermometer, salinometer, densitometer, myriameter, choreographer, piezometer, variometer, ovipositor, dynamometer, anemometer, katharometer, mass spectrometer, audiometer, mileometer, vinyl polymer, goniometer, galvanometer, sensitometer, inclinometer, actinometer, declinometer, tacheometer, magnetometer, atomic number, cardinal number, kentucky wonder, natural number, opposite number, parachute jumper, rational number, telephone number

6 syllables:
interferometer, autobiographer, accelerometer, cinematographer, sphygmomanometer, evaporometer, telethermometer, algebraic number, irrational number, registration number, transcendental number

7 syllables:
clinical thermometer, resistance thermometer, radiomicrometer, imaginary number

8 syllables:
electrodynamometer, identification number, pure imaginary number, social security number

9 syllables:
radio interferometer, bank identification number

12 syllables:
imaginary part of a complex number