Treading
Walking, here with connotations of walking heavily
Toll
Verb for the ringing sound produced by a bell, specifically
Solitary
Alone, single, or secluded/isolated. All of these meanings are relevant here.
Plank
A wooden board. Also, in extended usage, a central piece of a political or other ideological/policy platform, perhaps a pertinent secondary meaning in the context of this poem.
Plunge
To fall quickly and, usually, a substantial distance
