The answer is become.
Fallback is a compound word. Falloff and fallout are compound words.
teardrop gumdrop raindrop dewdrop backdrop
Doable
airtimeanytimebedtimedowntimelunchtimemealtimeovertimeplaytimesometimespringtimesummertimetimebasetimeouttimesharewintertime
zebralicious
One such word is whenever.
Balloon.
mousehouse
Bankteller
maidness
crossroadrailroadroadblockroadsignsroadsideroadwayroadrunnerroadworkroadworthy
roommate