vulcanism/ʹvulkəniz(ə)m/ noun

• theatre-in-the-round
• theatre of the absurd
• theatrical
• theatricals
• theatrics
• the awkward squad
• thebaine
• the ball is in your, his, etc court
• Theban
• thebe
• the bee's knees
• the best of three/five/etc.
• the best part of
• the better part of
• the bird has flown
• the birds and the bees
• the boot is on the other foot
• the bottom falls out of the market, etc
• the buck stops here
• theca
• the coast is clear
• thecodont
• the corridors of power
• the crack of doom
• the cut of somebody's jib