Answer: stymy

AnswerCrossword Clue
STYMYThwart
STYMYMinor but insurmountable obstacle: Var.
STYMYBlock: Var.
STYMYFrustrate, alternatively
STYMYThwart: var.
stymyto hinder or obstruct
stymyto thwart, also STYMIE, STIMY