feeble
The old woman is too feeble to do her own shopping.
flap
Everything was working smoothly, there was no flap.
flip
She flipped through the pages of a magazine, not really concentrating on them.
fragile
This old glass dish is very fragile.
friction
Friction between two sticks can create a fire.
fuse
Their common interests fuse the two companies.
galaxy
Astronomers at the University of California discovered one of the most distant galaxies.
generalize
You cannot generalize about the effects，of the drug from one or two cases.