Connections Hint Today Wed, Jul 30 #817

Need help with Connections puzzle #817 on Wed, Jul 30? Get your daily connections hint today! Find the hidden links between these 16 words: COACH, DIRECT, GUIDE, TRAIN, INSTRUMENT, MEDIUM, ORGAN, VEHICLE, DIOXIDE, MONORAIL, TETRACYCLINE, TRIANGLE, ABUT, BULGE, GROAN, VOILA