Seminal
Formative, original
Predicament
Plight, difficulty
Undulate
Flow, surge
Hiatus
Pause, interval
Stoic
Apathetic, impassive
Incumbent
Necessary, mandatory
Solvent
Secure, solid
Equanimity
Composure, calm
Ruminate
Consider, contemplate
Tenacity
Determination, persistence
Punitive
Disciplinary
Insurgent
Revolutionary, rebel
Harrowing
Acutely distressing
Encumbrance
Obstacle, restraint
Evanescent
Fleeting, momentary
Crescendo
Gradual increase in sound