The Etymologies seem to list this word as a noun, but it is clearly the third person singular of the verb
Noldorin
tôl
verb. (he) comes
tôg
verb. (he) leads, brings
tol-
verb. to come
lhâf
verb. (he) licks
lhôd
verb. (he) floats
blâb
verb. (he) flaps, beats
lhammas
noun. account of tongues
orthor
verb. (he) masters, conquers
osgar
verb. (he) cuts, amputates
síla
verb. (he) shines white
sôg
verb. (he) drinks
thia
verb. it appears
tol-
verb. to come
According to WJ/301, the expression tôl acharn "vengeance comes" was later changed to tûl acharn by Tolkien