Beachhead, bearskin, bedpan, bedroom, bedspread, beefless, beeswax, befriend, bellhop, beltless and beltway are compound words. They begin with the letters be.
Fallback is a compound word. Falloff and fallout are compound words.
The answer is become.
A compound word starting with "drop" is "dropkick."
Doable
zebralicious
One such word is whenever.
airtimeanytimebedtimedowntimelunchtimemealtimeovertimeplaytimesometimespringtimesummertimetimebasetimeouttimesharewintertime
Balloon.
maidness
mousehouse
Bankteller
Snail