straitlaced or straightlacedadj

• three-quarter back
• three quarters
• three-ring circus
• three R's
• threescore
• threesome
• three-spined stickleback
• three strikes
• three-wheeler
• thremmatology
• threnode
• threnody
• threonine
• thresh
• thresher
• threshold
• threw
• thrice
• thrift
• thrifty
• thrill
• thriller
• thrills and spills
• thrips
• thrive