‘To nip in the bud’ is an idiom. To nip ‘means ‘to squeeze sharply’. When a bud is nipped, it will not develop into a flower and then into fruit. When something is nipped in the bud, it is destroyed in its early stages. It is prevented from growing any further. So ‘to nip in the bud’ means to destroy something at the very beginning.
For example:
Bad habits must be nipped in the bud.
Her plans for further studies were nipped in the bud.
His tendency to lie must be nipped in the bud.