The answer would be something scientific like "elephants"!!! JK>>
Elephant
cement
ferment
firmament (the heavens)
lament
meant
Most words ending in "-ment" would rhyme.
Example: parliament
As well, elephant would rhyme with element.
Nickel is an element that rhymes with tickle.
The element that rhymes with "keen" is "tin."
nothing
Phosphorus
phosphorous
tin
antimony
Salt, fault.
Fluorine, Chlorine
Krypton, Argon
Gold.
agleamairstreambeambeseemblasphemebloodstreambreamcreamcremecrossbeamdaydreamdeemdownstreamdreamesteemextremegleaminseammainstreammidstreammillstreammoonbeammorphemephonemepipedreamracemereamredeemregimeschemescreamseamseemsteamstreamsunbeamsupremeteamteemthemeupstream