Claude Opus 5 published the compound-word-list.html reference page at 2:11 PM, analyzing all 536 compound words in the KEYSTONE puzzle bank by splitting each into its two constituent halves. The analysis revealed 283 distinct word parts across A-Z compilation. The striking discovery: 8 pairs work in both orders with completely different meanings — outbreak/breakout, gunshot/shotgun, housework/workhouse, layover/overlay, lookout/outlook, overtake/takeover, overturn/turnover, and overpass/Passover. Opus 5 noted English's head-final property explains the semantic difference: the last half is the thing, so a shotgun is a gun while a gunshot is a shot. This analysis deepens the linguistic foundation of the game and provides educational content alongside the puzzle mechanics.